noun
swallowing whole; gulping down
Literally swallowing food without chewing, like a cormorant (鵜). Often used in the set phrase 鵜呑みにする.
彼は魚を鵜呑みにした。
He swallowed the fish whole.
You shouldn't swallow his story without question.
ネットの情報を鵜呑みにするのは危険だ。
It's dangerous to accept online information uncritically.
丸呑み also means swallowing whole, but it lacks the figurative sense of uncritical acceptance that 鵜呑み carries.
From 鵜 (cormorant) + 呑み (swallowing), referring to the way cormorants swallow fish whole. The figurative sense developed from the literal image of swallowing without chewing.