Synonyms for Loon:

n.

eccentric, crazy, weirdie, crank, lunatic, dipper, ding-a-ling, grebe, weirdo, loony, kook, nut, dingbat, wise, screwball. oddball, space cadet, nutjob, madman, headcase, madwoman, oddity. animal (noun)
diver.
bird (noun)
goldfinch, grosbeak, barn owl, penguin, buzzard, lark, hawk, harrier, cassowary, stork, duck, cardinal, puffin, flamingo, bird, ostrich, goose, quetzal, macaw, nuthatch, cockatoo, peregrine, songbird, dodo, sea gull, pheasant, canary, eagle, heron, myna, lovebird, coot, Canada Goose, cuckoo, blue jay, robin, swan, chickadee, magpie, swift, road runner, sheldrake, mourning dove, wren, squab, redbird, albatross, grackle, peacock, bald eagle, parrot, bluebill, curlew, crane, turtledove, teal, kingfisher, spoonbill, crested jay, crow, starling, jackdaw, pelican, osprey, snipe, jay, oriole, yellowbird, parakeet, plover, pigeon, dove, finch, raven, mockingbird, ringtail, rook, sandpiper, hummingbird, blackbird, ibis, mallard, horned owl, nightingale, owl, redwing, gull, bittern, turkey, tern, booby, weaver, emu, bluebird, vulture, cormorant, condor, grouse, thrush, partridge, woodpecker, bullfinch, waxwing, sparrow, egret, falcon.
crackpot (noun)
nut, crazy, lunatic, eccentric.
fool (noun)
cretin, nitwit, dullard, dimwit, blockhead, crackpot, dolt, fool, imbecile, dummy, clod, ignoramus, chuckle-head, meathead, lame-brain, simpleton, half-wit, bonehead, dumbbell, nincompoop, dunce, bungler, knuckle-head, moron.
loon (noun)
diver, addle-head, birdbrain.

Other synonyms:

screwball, ding-a-ling, dingbat, weirdo, weirdie. kook. loony. lunatic. nut, crank, crazy. Other relevant words:
crazy, ding-a-ling, birdbrain, eccentric, crank, kook, loony, dingbat, addle-head, nut, diver, nutjob, screwball, lunatic, madman, weirdo, weirdie.

Usage examples for loon

  1. She's crazy, crazy as a loon – The Land of Long Ago by Eliza Calvert Hall