† pentacanthousadj. [ < penta-comb. form + ancient Greek ἄκανθα thorn (see acanthusn.) + -oussuffix, after scientific Latin pentacanthus (1790 or earlier as a specific epithet)] ZoologyObsoleterare having five spines.Apparently only attested in dictionaries or glossaries.
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1857 R. G. MayneExpos. Lexicon Med. Sci. (1860) Pentacanthus, applied to a fish with five spinous rays to one of its fins..:pentacanthous.