Tribulation, n.
Etymology: [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. When tribulation or persecution ariseth because of the word, by and by he is offended. Matt. xiii. 21. In the world ye shall have tribulation. John. xvi. 33.
Shades of meaning
Fernald has no entry of its own for tribulation; he lists it under grief, misfortune.
Where he writes about it:
Affliction, chastening, trial, and tribulation have all an especially religious bearing, suggesting some disciplinary purpose of God with beneficent design. — from misfortune
Affliction may be keen and bitter, but brief; tribulation is long and wearing. — from misfortune
We speak of an affliction, but rarely of a tribulation, since tribulation is viewed as a continuous process, which may endure for years or for a lifetime; but we speak of our daily trials. — from misfortune