lament vs lamentation

lament and lamentation both are nouns.

Word	Noun	Adjective	Verb	Adverb
lament	Yes	No	Yes	No
lamentation	Yes	No	No	No

As nouns, lament and lamentation are synonyms defined as:

Other synonyms of lament include plaint, wail.

lament (noun)	lamentation (noun)
a mournful poem; a lament for the dead	the passionate and demonstrative activity of expressing grief
a song or hymn of mourning composed or performed as a memorial to a dead person	a cry of sorrow and grief
a cry of sorrow and grief

lament (verb)	lamentation (verb)
regret strongly
express grief verbally