the word 'thornless' is a straightforward english compound formed by combining the noun 'thorn' with the suffix '-less'. 'thorn' has deep germanic roots, tracing back to proto-germanic þurnuz and ultimately to the proto-indo-european root (s)ter-, meaning 'stiff, rigid'. the suffix '-less' originates from the old english adjective lēas, meaning 'devoid of', which itself evolved from a noun meaning 'loss'. the logic of the word is entirely transparent in modern english: it literally describes a plant that is 'devoid of thorns', directly conveying the absence of the sharp, protective structures found on species like roses or blackberries.

Structure: thorn (sharp point on a plant) + less (without) thorn: from old english þorn, of germanic origin; a noun meaning a stiff, sharp-pointed projection on a plant. less: from old english -lēas, an adjective-forming suffix meaning 'devoid of, free from'.