Synonyms for Casual:

adj.

accidental (adjective)
adventitious, fortunate, purposeless, coincidental, accidental, unintentional, causeless, fluky, fortuitous, fatal, aimless, unexpected, chance, random, lucky, haphazard.
all (adjective)
insouciant, nonchalant, Fooling.
chance (adjective)
fluky.
chance, random (adjective)
infrequent, unintentional, fortuitous, spontaneous, odd, unexpected, irregular, erratic, accidental, fluky, occasional, unplanned, contingent, adventitious, impromptu.
colloquial (adjective)
conversational, vernacular, informal, slang, idiomatic, colloquial.
good-humored (adjective)
easy.
inattentive (adjective)
careless.
irregular (adjective)
irregular.
nonchalant, relaxed in manner (adjective)
folksy, unconcerned, insouciant, lackadaisical, cursory, perfunctory, purposeless, laid-back, informal, indifferent, cool, easygoing, apathetic.
offhand (adjective)
folksy.
succinct (adjective)
direct, Plain-spoken, blunt, frank, prosaic, stark, honest, straightforward, clear, outspoken, unadorned, candid, unpoetical, informal, unpretentious, ordinary, folksy, uncluttered, intelligible, bald, simple.
talkative (adjective)
conversational.
unnecessary (adjective)
causeless.

n.

coincidental, inadvertent, arbitrary, by accident, contingent, impromptu, surprise, involuntary, odd, instinctive. deputy, unrestrained, creative, relaxed, designate, plain, tighten, acting, spontaneous, budding, emeritus, auxiliary, natural, easygoing, unceremonious, laid-back, blue-collar. affective, depth, blind, bitter, deep, burning, basic, deep-seated, acutely. antisocial, cooperative, ceremonial, associate, collaborative, clerical, assistant, collegiate, adjunct. lackadaisical, slipshod, remiss, like a bull in a china shop, complacency. calm, cool, at one with, composed, chilled, at ease. from time to time, sometimes, occasionally, (every) now and then/again, every so often. casual (noun)
insouciant, light, everyday, careless, easy, free-and-easy, unplanned, nonchalant, occasional, cursory, irregular, chance, Fooling, accidental, passing, perfunctory, informal, unconcerned, effortless.
informal (noun)
easygoing, relaxed, unceremonious.
nonchalant (noun)
apathetic, indifferent.
occasional (noun)
erratic, infrequent.

Other synonyms:

auxiliary, easygoing, clerical, blind, deep, coincidental, bitter, deputy, assistant. adjunct, relaxed, cooperative, inadvertent, depth, burning, associate. contingent, unrestrained. odd. natural. fooling
Fooling.
informal
unceremonious.
involuntary
spontaneous.

Usage examples for casual

  1. " I confess," replied Legrand, " that the matter still wears a serious aspect, when regarded with a casual glance. – Selections From Poe by J. Montgomery Gambrill
  2. It was no casual glance, he gave the names. – The Rat Racket by David Henry Keller
  3. He looked around, not quickly nor directly, but in a casual manner; taking fully a minute over the process. – The Heath Hover Mystery by Bertram Mitford