monologue vs actor's line

monologue and actor's line both are nouns.

Word	Noun	Adjective	Verb	Adverb
monologue	Yes	No	No	No
actor's line	Yes	No	No	No

As nouns, actor's line is a hypernym of monologue; that is, actor's line is a word with a broader meaning than monologue:

Other hypernyms of monologue include speech, words.

monologue (noun)	actor's line (noun)
speech you make to yourself	words making up the dialogue of a play
a (usually long) dramatic speech by a single actor
a long utterance by one person (especially one that prevents others from participating in the conversation)