na-adjective, noun which may take the genitive case particle 'no', noun
obvious; clear as day; plain to see
A yojijukugo meaning something is so clear that one glance is enough to understand it. Often used in formal or written contexts.
彼の嘘は一目瞭然だった。
His lie was obvious at a glance.
The result is clear as day and leaves no room for debate.