gadol, gaw-dole’; from <H1431> (gadal); great (in any sense); hence older; also insolent :- + aloud, elder (-est), + exceeding (-ly), + far, (man of) great (man, matter, thing, -er, -ness), high, long, loud, mighty, more, much, noble, proud thing, × sore, (×) very. Strong’s Talking Greek & Hebrew Dictionary.

The GREAT DAY of the LORD is a phrase used in the Bible for the End Times and/or the Tribulation period.

a day (as the warm hours), whether literal (from sunrise to sunset, or from one sunset to the next), or figurative (a space of time defined by an associated term), [often used adverbially] :- age, daily, ([birth-], each, to) day, (now a, two) days (agone), × end, + evening, + (for) ever (-lasting, -more), season, space, then, (process of) time, + as at other times, + in trouble, (full) year (-ly). Strong’s Talking Greek & Hebrew Dictionary.

or qol, kole; from an unused root meaning to call aloud; a voice or sound :– + aloud, bleating, crackling, cry (+ out), fame, lightness, lowing, noise, + hold peace, [pro-] claim, proclamation, + sing, sound, + spark, thunder (-ing), voice, + yell. Strong’s Talking Greek & Hebrew Dictionary.

Tsarach- H6873-a primitive root; to be clear (in tone, i.e. shrill), i.e. to whoop :- cry, raise a war cry; war cry.
Strong’s Talking Greek & Hebrew Dictionary.

*This word only appears twice in the OT. Zephaniah 1:14 and Isaiah 42:13.

Isaiah 42:13-The Lord will march forth like a mighty man. He will stir up his zeal like a warrier. He will shout! Indeed, he will raise a war cry! He will prevail against his enemies.

marah, maw-raw’; from <H4843> (marar); bitter (literal or figurative); also (as noun) bitterness, or (adverb) bitterly :- + angry, bitter (-ly, -ness), chafed, discontented, × great, heavy. Strong’s Talking Greek & Hebrew Dictionary.

Ebra-feminine of <H5676> (`eber); an outburst of passionate anger, rage, wrath.
Strong’s Talking Greek & Hebrew Dictionary.

Sara-feminine of <H6862> (tsar); tightness (i.e. figurative trouble); a female rival :- adversary, adversity, affliction, anguish, distress, tribulation, trouble. Strong’s Talking Greek & Hebrew Dictionary.

show’ah, sho-aw’; or sho’ah, sho-aw’; from an unused root meaning to rush over; a tempest; by implication devastation :- desolate (-ion), destroy, destruction, storm, wasteness. Strong’s Talking Greek & Hebrew Dictionary.

mesho’ah, mesh-o-aw’; from the same as <H7722> (show’); (a) ruin, abstract (the act) or concrete (the wreck) :- desolation, waste. Strong’s Talking Greek & Hebrew Dictionary.

from <H2821> (chashak); the dark; hence (literal) darkness; figurative misery, destruction, death, ignorance, sorrow, wickedness :- dark (-ness), night, obscurity. Strong’s Talking Greek & Hebrew Dictionary.

Arapel-probably from <H6201> (`araph); gloom (as of a lowering sky) (thick) dark cloud (-ness).
Strong’s Talking Greek & Hebrew Dictionary.

This word is also used to describe God coming down from above, in a cloud, to interact with humans.

Exodus 20:21 (KJV)
And the people stood far off, and Moses drew near to the thick darkness where God was.

Deuteronomy 4:11-12 (KJV)
And you came near and stood under the mountain; and the mountain burned with fire into the midst of heaven, with darkness, clouds, and thick darkness. Then, the LORD spoke to you out of the midst of the fire. You heard the voice speaking the words to obey, but saw no embodiment (image). You only heard a voice.

2 Samuel 22:10-15 (KJV)
He bowed the heavens also, and came down; and darkness was under his feet. And he rode upon a cherub, and did fly: and he was seen upon the wings of the wind. And he made darkness pavilions round about him, dark waters, and thick clouds of the skies. Through the brightness before him were coals of fire kindled. The LORD thundered from heaven, and the most High uttered his voice. And he sent out arrows, and scattered them; lightning, and discomfited them.

1 Kings 8:10-11 (KJV)
And it came to pass, when the priests were come out of the holy place, that the cloud filled the house of the LORD,
So that the priests could not stand to minister because of the cloud: for the glory of the LORD had filled the house of the LORD.

or shophar, sho-far’; from <H8231> (shaphar) in the original sense of incising; a cornet (as giving a clear sound) or curved horn :- cornet, trumpet. Strong’s Talking Greek & Hebrew Dictionary.

Teruah-from <H7321> (ruwa`); clamor, i.e. acclamation of joy or a battle-cry; especially clangor of trumpets, as an alarum :- alarm, blow (-ing) (of, the) (trumpets), joy, jubile, loud noise, rejoicing, shout (-ing), (high, joyful) sound (-ing). Strong’s Talking Greek & Hebrew Dictionary.

Yom Teruah is a is an appointed time; a moed in Judiasm. It is a day to remember Jehovah with the blowing of trumpets in preparation for the upcoming Day of Atonement (Yom Kipper). Yom Teruah is scheduled on the same day as Rosh Hashanah; another appointed time or moed. (Lev 23:23-25; Num 29:1-6)

Revelation 14:14-20 (KJV)
I looked, and behold a white cloud, and upon the cloud one sat like unto the Son of man, having on his head a golden crown, and in his hand a sharp sickle. And another angel came out of the temple, crying with a loud voice to him that sat on the cloud, “Thrust in thy sickle, and reap: for the time is come for thee to reap; for the harvest of the earth is ripe.” So, he that sat on the cloud thrust in his sickle on the earth; and the earth was reaped.

Then, another angel came out of the temple which is in heaven, he also having a sharp sickle. And another angel came out from the altar, which had power over fire; and cried with a loud cry to him that had the sharp sickle, saying, “Thrust in thy sharp sickle, and gather the clusters of the vine of the earth; for her grapes are fully ripe. So, the angel thrust in his sickle into the earth, and gathered the vine of the earth, and cast it into the great winepress of the wrath of God. And the winepress was trodden outside the city, and blood came out of the winepress, even unto the horse bridles, by the space of a thousand and six hundred furlongs.

Pinna-feminine of <H6434> (pen); an angle; by implication a pinnacle; figurative a chieftain :- bulwark, chief, corner, stay, tower, cornerstone. Strong’s Talking Greek & Hebrew Dictionary.

Isaiah 28:16 (KJV)
The Lord GOD says, “Behold, I lay a stone in Zion, a tried stone, a precious corner stone, a sure foundation: he that believes shall not make haste”.

from <H3700> (kacaph); silver (from its pale color); by implication money :- money, price, silver (-ling).
Strong’s Talking Greek & Hebrew Dictionary.

from an unused root meaning to shimmer; gold; figurative something gold-colored (i.e. yellow), as oil, a clear sky :- gold (-en), fair weather. Strong’s Talking Greek & Hebrew Dictionary.

Eres-from an unused root probably meaning to be firm; the earth (at large, or partitively a land) :- × common, country, earth, field, ground, land, × nations, way, + wilderness, world. Strong’s Talking Greek & Hebrew Dictionary.

from <H7065> (qana’); jealousy or envy :- envy (-ied), jealousy, × sake, zeal.
Strong’s Talking Greek & Hebrew Dictionary.

Ezekiel 36:5-6 (KJV)
Therefore, thus saith the Lord GOD, “Surely, in the fire of my jealousy, have I spoken against the remainder of the heathen (gentiles), and against all Edom, who took my land into their possession with joy in their hearts and with contempt in their souls; planning to cast out (my flock or people) and plunder.

Proverbs 6:34-35 (KJV)
The jealous wrath of a mighty warrior will not show compassion (pity) in the day of vengeance. He will not accept a ransom (redemption-price) from anyone, neither will he be willing to accept an increase in donations (venal or redemptive) .

a primitive root; to tremble inwardly (or palpitate), i.e. (figurative) be (causative make) (suddenly) alarmed or agitated; by implication to hasten anxiously :- be (make) (afraid, amazed, dismayed, rash), (be, get, make) haste (-n, -y, -ily), (give) speedy (-ily), thrust out, trouble, vex. Strong’s Talking Greek & Hebrew Dictionary.

from <H3615> (kalah); a completion; adverb completely; also destruction :- altogether, (be, utterly) consume (-d), consummation (-ption), was determined, (full, utter) end, riddance. Strong’s Talking Greek & Hebrew Dictionary.