The noun has one meaning:
Meaning #1:
someone deranged and possibly dangerous
Synonyms: crazy, looney, weirdo
The adjective loony has one meaning:
Meaning #1:
informal or slang terms for mentally irregular
Synonyms: balmy, barmy, bats, batty, bonkers, buggy, cracked, crackers, daft, dotty, fruity, haywire, kooky, kookie, loco, loopy, nuts, nutty, round the bend, around the bend, wacky, whacky
