nonchalance noun
ADJ. cool
VERB + NONCHALANCE affect, feign, pretend She shrugged, feigning nonchalance.
PREP. with ~ declining the offer with cool nonchalance
PHRASES an air of nonchalance ‘Oh, by the way … ’ she started, with a false air of nonchalance.
You can also check other dicts: nonchalance (English, 中文解释 ), wordnet sense, Collins Definition