The Collaborative International Dictionary of English v.0.48:

Tribulation \Trib`u*la"tion\, n. [OE. tribulacium, F.
   tribulation, L. tribulatio, from tribulare to press, afflict,
   fr. tribulum a thrashing sledge, akin to terere, tritum, to
   rub. See Trite.]
   That which occasions distress, trouble, or vexation; severe
   affliction.
   [1913 Webster]

         When tribulation or persecution ariseth because of the
         word, by and by he is offended.          --Matt. xiii.
                                                  21.
   [1913 Webster]

         In the world ye shall have tribulation.  --John. xvi.
                                                  33.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tribulation
    n 1: an annoying or frustrating or catastrophic event; "his
         mother-in-law's visits were a great trial for him"; "life
         is full of tribulations"; "a visitation of the plague"
         [syn: trial, tribulation, visitation]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "tribulation":
   adverse circumstances, adversity, affliction, aggravation,
   annoyance, blight, bummer, calvary, care, cross, crucible, curse,
   difficulties, difficulty, downer, fiery ordeal, hard knocks,
   hard life, hard lot, hardcase, hardship, irritation, oppression,
   ordeal, persecution, plight, predicament, pressure, rigor,
   sea of troubles, stress, stress of life, trial,
   trials and tribulations, trouble, troubles, vale of tears,
   vicissitude, visitation



Easton's 1897 Bible Dictionary:

Tribulation
   trouble or affiction of any kind (Deut. 4:30; Matt. 13:21; 2
   Cor. 7:4). In Rom. 2:9 "tribulation and anguish" are the penal
   sufferings that shall overtake the wicked. In Matt. 24:21, 29,
   the word denotes the calamities that were to attend the
   destruction of Jerusalem.