think vs imagine

think is a noun but imagine is not a noun.

Word	Noun	Adjective	Verb	Adverb
think	Yes	No	Yes	No
imagine	No	No	Yes	No

As verbs, think and imagine are synonyms defined as:

Other synonyms of think include guess, opine, reckon, suppose.

As verbs, imagine is a hypernym of think; that is, imagine is a word with a broader meaning than think:

think: imagine or visualize
imagine: form a mental image of something that is not present or that is not the case

Other hypernyms of think include conceive of, envisage, ideate.

think (noun)	imagine (noun)
an instance of deliberate thinking

think (verb)	imagine (verb)
bring into a given condition by mental preoccupation	expect, believe, or suppose
use or exercise the mind or one's power of reason in order to make inferences, decisions, or arrive at a solution or judgments	form a mental image of something that is not present or that is not the case
judge or regard; look upon; judge
recall knowledge from memory; have a recollection
expect, believe, or suppose
have in mind as a purpose
be capable of conscious thought
focus one's attention on a certain state
decide by pondering, reasoning, or reflecting
ponder; reflect on, or reason about
have or formulate in the mind
dispose the mind in a certain way
imagine or visualize