lamentation vs plaint

lamentation and plaint both are nouns.

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

As nouns, lamentation and plaint are synonyms defined as:

Other synonyms of lamentation include lament, wail.

lamentation (noun)	plaint (noun)
the passionate and demonstrative activity of expressing grief	a cry of sorrow and grief
a cry of sorrow and grief	(United Kingdom) a written statement of the grounds of complaint made to court of law asking for the grievance to be redressed