The word 'unfruitful' is a layered English construction. Its core, 'fruit,' descends from Latin fructus, which itself evolved from the verb frui (to enjoy, have the use of), carrying a sense of productive yield or benefit. The suffix '-ful,' of Old English origin, was attached to create 'fruitful,' meaning "abounding in fruit" or "productive." Finally, the Old English negative prefix 'un-' was prefixed to form the opposite, 'unfruitful.' Thus, the word's logic moves from the ancient concept of enjoyment and yield, through the idea of being full of that yield, to its modern negation, describing something that lacks productive results.

Structure: un (not) + fruit (fruit/produce) + ful (full of/having) - un: A prefix of Germanic origin (Old English un-), meaning "not." It functions as a negative particle. - fruit: A noun of Latin origin (via Old French), from Latin fructus meaning "enjoyment, produce, fruit." It functions as the core semantic root. - ful: A suffix of Germanic origin (Old English -ful), meaning "full of" or "characterized by." It functions to form adjectives from nouns.