Spiny means covered with sharp points. A spiny shell, spiny leaves, a spiny fish.
The points are defence and sometimes venom: many spiny fish carry it in the spines, which is why a wound from one hurts long after it should. In plants, spines are modified leaves and thorns are modified stems — a real distinction that gardeners ignore.
1adjectivespinyCovered with sharp points.
“Be careful picking up that sea urchin; it's very spiny.”
spiny is a quality of surface.
Proto-Indo-European
*spey-
Latin
spīna — a thorn; a prickle, spine; the backbone
Old French
espine
Middle English
spyne
English
spine
English, today
spiny
From spine + -y. spine comes from late Middle English spyne, from Old French espine (French épine) or its source, Latin spīna (“a thorn; a prickle, spine; the backbone”). a doublet of spina.
Etymology from Wiktionary, CC BY-SA