gainful

The word 'gainful' is a relatively transparent English formation. Its core, 'gain', entered Middle English from Old Norse 'gagn', meaning "advantage" or "benefit", which itself traces back to a Proto-Germanic root conveying the idea of a return or yield. The adjectival suffix '-ful', of native Old English origin, means "full of" or "characterized by". Thus, the literal construction "full of gain" directly and logically evolved into the modern abstract meaning of "profitable" or "yielding positive returns", specifically applied to employment or activity.

Structure: gain (to acquire) + ful (full of) - gain: From Middle English 'gaynen', meaning "to be of use, profit, avail". Of Old Norse origin, from 'gagn' (advantage, use). - ful: A suffix forming adjectives, from Old English '-ful', meaning "full of".