فهو اللفظ المستعمل فيما شبه بمعناه الأصلي
It is an expression used for something resembling its original meaning.
Here “expression” can mean a complete construction, rather than one isolated word. Its original meaning is the state of affairs ordinarily conveyed by the whole expression; in another context the utterance may represent a similar state of affairs.
This formulation particularly suits representative metaphor (istiʿārah tamthīliyyah). A further question arises in the commentary: not every figurative use of a compound is based on resemblance, so a resemblance-based formulation cannot automatically exhaust the wider genus.