the word 'spiny' is a straightforward english formation, combining the noun 'spine' with the adjectival suffix '-y'. the root 'spine' originates from the latin 'spina', which referred to a thorn, prickle, or the backbone of an animal. this latin term is thought to be derived from a proto-indo-european root meaning 'sharp point'. the suffix '-y', of old english origin, is a highly productive morpheme used to create adjectives meaning 'having the qualities of' or 'full of'. therefore, the literal construction 'full of spines' directly and logically evolved into the modern meanings describing something physically covered in sharp points or, metaphorically, something difficult and prickly to deal with.

Structure: spin(e) (thorn) + y (adjective suffix) spine (from latin 'spina', meaning thorn, backbone) + y (from old english '-ig', forming adjectives meaning 'full of' or 'characterized by')