As an interrogative marker introducing a question. regional and nonstandard in later use.

Chiefly qualifying an adjective or adverb: To what extent? In what degree? (Also with the verb like, or an equivalent.)

elliptical for ‘How is it?’ or ‘How say you?’ and used interjectionally, the modern equivalent being ‘What?’ or ‘What!’ (= French quoi!) archaic…

Interrogatively = ‘Is it so?’ ‘Really?’

Used parenthetically. Interrogatively, expressing surprise or doubt.

Used for emphasis at the end of a question; ‘may I ask?’, ‘would you say?’; = anyway, adv. 2b.

how's about? = how about at sense A. 4a. colloquial (chiefly U.S.).