The story
From diaper (“an absorbent garment”) + suit (“a garment or set of garments suitable and/or required for a given task or activity”).
Etymology from Wiktionary, CC BY-SA 4.0.
diapersuit
dia·per·suitToday it means: In fiction and art, an insulated full-body suit, usually made out of rubber or latex, that either functions entirely like a diaper or includes a diaper attached within it; sometimes depicted as a mascot-like costume. Full definition →