second hand vs go-between

second hand and go-between both are nouns.

Word	Noun	Adjective	Verb	Adverb
second hand	Yes	No	No	Yes
go-between	Yes	No	No	No

As nouns, go-between is a hypernym of second hand; that is, go-between is a word with a broader meaning than second hand:

Other hypernyms of second hand include intercessor, intermediary, intermediator, mediator.

second hand (noun)	go-between (noun)
hand marking seconds on a timepiece	a negotiator who acts as a link between parties
an intermediate person; used in the phrase `at second hand'

second hand (adverb)	go-between (adverb)
from a source of previously owned goods