window sash vs casement

window sash and casement both are nouns.

Word	Noun	Adjective	Verb	Adverb
window sash	Yes	No	No	No
casement	Yes	No	No	No

As nouns, casement is a hyponym of window sash; that is, casement is a word with a more specific, narrower meaning than window sash:

window sash: a framework that holds the panes of a window in the window frame
casement: a window sash that is hinged (usually on one side)

window sash (noun)	casement (noun)
a framework that holds the panes of a window in the window frame	a window sash that is hinged (usually on one side)