expression, godan verb (-su)
feather one's own nest; line one's pockets
Idiomatic expression meaning to enrich oneself, often through dishonest or selfish means.
彼は公金を使って懐を肥やした。
He lined his pockets using public funds.
The expression combines 懐 (ふところ, 'bosom' or 'pocket') with 肥やす (こやす, 'to fatten' or 'to enrich'), literally meaning 'to fatten one's pocket'.