lour vs grimace

lour is not a noun while grimace is a noun.

Word	Noun	Adjective	Verb	Adverb
lour	No	No	Yes	No
grimace	Yes	No	Yes	No

As verbs, grimace is a hypernym of lour; that is, grimace is a word with a broader meaning than lour:

lour: look angry or sullen, wrinkle one's forehead, as if to signal disapproval
grimace: contort the face to indicate a certain mental or emotional state

Other hypernyms of lour include make a face, pull a face.

lour (noun)	grimace (noun)
	a contorted facial expression

lour (verb)	grimace (verb)
look angry or sullen, wrinkle one's forehead, as if to signal disapproval	contort the face to indicate a certain mental or emotional state
make lower or quieter
set lower