Marked by blithe unconcern:
— Drove his car with nonchalant abandon.
— Was polite in a teasing nonchalant manner.

synonyms: casual, insouciant.

Roget 823: insensible, unconscious; impassive, impassible; blind to, deaf to, dead to; unsusceptible, insusceptible; unimpressionable^†, unimpressible^†; passionless, spiritless, heartless, soulless; unfeeling, unmoral.    apathetic; leuco-^†, phlegmatic; dull, frigid; cold blooded, cold hearted; cold as charity; flat, maudlin, obtuse, inert, supine, sluggish, torpid, torpedinous^†, torporific^†; sleepy etc. (inactive) 683; languid, half-hearted, tame; numbed; comatose; anaesthetic etc. 376; stupefied, chloroformed, drugged, stoned; palsy-stricken.    indifferent, lukewarm; careless, mindless, regardless; inattentive etc. 458; neglectful etc. 460; disregarding.    unconcerned, nonchalant, pococurante^†, insouciant, sans souci [Fr.]; unambitious etc. 866.    unaffected, unruffled, unimpressed, uninspired, unexcited, unmoved, unstirred, untouched, unshocked^†, unstruck^†; unblushing etc. (shameless) 885; unanimated; vegetative.    callous, thick-skinned, hard-nosed, pachydermatous, impervious; hardened; inured, casehardened; steeled against, proof against; imperturbable etc. (inexcitable) 826^†; unfelt.    ... show more