Noun second hand has 2 senses

• second hand(n = noun.person) Array - an intermediate person; used in the phrase `at second hand'; "he could learn at second hand from books"
is a kind of go-between, intercessor, intermediary, intermediator, mediator

• second hand(n = noun.artifact) Array - hand marking seconds on a timepiece; Array
is a kind of hand
has particulars: sweep-second, sweep hand

Adverbial second hand has 1 sense

• second hand(r = adv.all) Array - from a source of previously owned goods; "I prefer to buy second hand"