thornback noun5 •Any animal with a thorny back, especially marine animals. •The thornback guitarfish (Platyrhinoidis triseriata), a species of ray in the north-eastern Pacific Ocean. •The thornback ray or thornback skate (Raja clavata), a species of ray in the Atlantic Ocean. •The thornback skate (Dentiraja lemprieri), a fish endemic to Australia. •(no longer used) A woman over a certain age (variously 26 or 30) who has never married, older than a spinster.[A] society of honest gentlemen [is holding a lottery] for the benefit of all single ladies, widows, maids, or thornbacks […] — 1710 formsthornbacks
