A variant or archaic term for a small fish or finned creature; a dialectal word rarely used in modern English.
From fin plus a diminutive or descriptive suffix, possibly '-ip' (a Scandinavian or Germanic diminutive ending). This appears to be an obsolete or highly regional term with uncertain documentation.
Words like 'finnip' are language fossils—they exist in old texts and dialects but have been almost completely replaced by newer terms, and nobody's quite sure what they originally meant!
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