Here are the list of the civilians that were murdered by Irgun.
List of Irgun attacks
1938, June 26 7 Arabs were killed by a bomb in Jaffa.
1938, July 5 7 Arabs were killed in several shooting attacks in Tel-Aviv.
1938, July 16 10 Arabs were killed by a bomb at a marketplace in Jerusalem.
1938, July 25 43 Arabs were killed by a bomb at a marketplace in Haifa.
1938, August 26 24 Arabs were killed by a bomb at a marketplace in Jaffa.
1939, February 27 33 Arabs were killed in multiple attacks, in Arab market in Suk Quarter of Haifa and market in Jerusalem.
1939, June 19 20 Arabs were killed by explosives mounted on a donkey at a marketplace in Haifa.
1946, July 22 91 people were killed at King David Hotel Bombing mostly civilians, staff of the hotel or Secretariat
1947, December 12 20 killed, 5 wounded by barrel bomb at Damascus Gate.
1947, December 29 14 Arabs killed by bomb in Jerusalem.
1948, January 7 20 Arabs killed by bomb at Jaffa Gate.
1948, February 18 12 Arabs killed and 43 wounded at a marketplace in Ramla
1948, March 1 20 Britons killed and 30 wounded in the Bevingrad Officers Club bombing
1948, April 9-April 11 107-120 Palestinians killed and massacred during and after the battle at the village of Deir Yassin
Full List:
List of Irgun attacks - Wikipedia, the free encyclopedia
Deir Yassin massacre
Around 107 villagers were killed during and after the battle for the village, including women and children—some were shot, while others died when hand grenades were thrown into their homes. Several villagers were taken prisoner and may have been killed after being paraded through the streets of West Jerusalem, though accounts vary.
Full Text:
Deir Yassin massacre - Wikipedia, the free encyclopedia
Bombing markeplaces with bombs attached to donkeys...
Attacking hotels with bombs full of civilians...
Massacring civilian villagers who has no guns..
So yes. Irgun, unquestionably, was a terrorist organization.