pre-noun adjectival
similar but different; falsely similar; pseudo-
Fixed pre-noun adjectival (rentaishi) expression meaning something appears similar but is essentially different or spurious. Often used in formal or critical contexts.
それは似て非なるものだ。
That is something similar but essentially different.
似て非なる政策を掲げる政党が増えている。
Political parties advocating falsely similar policies are increasing.
A fixed expression combining 似て (te-form of 似る, 'resemble') and 非なる (archaic/formal attributive of 非ず, 'is not'), literally 'resembling but not being'. The exact historical derivation is uncertain, but it has been used as a set phrase since at least the early modern period.