Indifferent; careless; cool.

Etymologically, nonchalant comes from the French expression for "not hot under the collar." This is not the same thing, however, as being "cool," if by that term you mean blasé, sophisticated indifference. Nonchalance is instead a stylish form of engaged detachment. See: DETACHED, INDIFFERENT, INSOUCIANT.

marked by blithe unconcern; "an ability to interest casual students"; "showed a casual disregard for cold weather"; "an utterly insouciant financial policy"; "an elegantly insouciant manner"; "drove his car with nonchalant abandon"; "was polite in a teasing nonchalant manner"

a captivating, intoxicating individual