Which word is the closest in meaning to “insouciance” in the given context?

Question

Insouciance: His insouciance, which was kept in check by the law of custom, had its root, like most other evils, in selfishness

(a) apathy (b) lassitude (c) deceit (d) indecision

To me it apathy seems to be correct, but my instructor is of the opinion that lassitude is the correct one. Please explain.

Please Note: This sentence is taken from The Fijians: A Study of the Decay of Custom, chapter XIV, Page number -228, however we don't have access to this source at the time of solving.

Answer 1

The OED defines it as carelessness, indifference, unconcern. Collins Thesaurus offers these alternatives: nonchalance, light-heartedness, jauntiness, airiness, breeziness, carefreeness. Neither apathy nor lassitude seems quite to capture the affected air of effortless disdain which insouciance seems to imply. It’s crediting the word with too much to describe it as an evil. I suspect the writer didn’t really know what it meant but threw it in to give the sentence a faintly exotic cast.