total mismatch; ill-suited; square peg in a round hole
A yojijukugo literally meaning 'square base, round lid', used to describe things that are fundamentally incompatible or mismatched. Often used in formal or written contexts.
His proposal and our plan are a total mismatch.
This contract is ill-suited and benefits neither party.
不適合 is a more general term for incompatibility or non-conformity, while 方底円蓋 emphasizes a fundamental, almost geometric mismatch.
齟齬 refers to a discrepancy or inconsistency, often in details, whereas 方底円蓋 describes a complete and obvious lack of fit.
A yojijukugo composed of 方 (square), 底 (base), 円 (round), and 蓋 (lid). The literal image of a square base with a round lid that cannot close properly is used metaphorically to express a fundamental mismatch.