expression, noun-modifying (irregular)
Fixed expression describing someone or something as round and fat, often with a cute or endearing nuance. Used prenominally.
See also: 丸々太った
A chubby baby is smiling.
He has a plump cat.
From 丸々 (round, plump) + と (adverbial particle) + 太った (past form of 太る, to become fat). The expression is a fixed prenominal phrase.