plaint vs lamentation

plaint and lamentation both are nouns.

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

As nouns, plaint and lamentation are synonyms defined as:

Other synonyms of plaint include lament, wail.

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