noun, masculine/kal.sɔ̃/plural: caleçons
caleçon is masculine in French.
boxer shorts, boxer briefs
“Ce qui me le fit mettre dans les poches de mon caleçon de bain...” — Which made me put it in the pockets of my swimming trunks...
Related: caleçon de bain
Borrowed from Italian calzone, with an excrescent schwa (cf. the form calçon, attested in the sixteenth century). Doublet of chausson, an inherited form.