mostly

The word 'mostly' is a straightforward formation from the Middle English superlative 'most', which itself evolved from the Old English 'māst'. This Old English term is the superlative form of 'micel', meaning "great" or "much", tracing its lineage back to the Proto-Germanic 'maistaz' and ultimately to the Proto-Indo-European 'mey-' (meaning "great"). The adverbial suffix '-ly' originates from Old English '-līĉe', derived from the noun 'līc' meaning "body" or "form", which evolved to indicate "having the form or manner of". Therefore, the literal construction "in the manner of the greatest part" logically evolved into the modern abstract meaning of "mainly" or "for the most part", describing what is predominant or generally true.

Structure: most (greatest in amount/degree) + ly (adverb-forming suffix) - most: From Old English māst, superlative form of micel ("much, great"). Its functional role is as the base adjective/adverb meaning "greatest in amount or degree". - ly: From Old English -līċe, an adverbial suffix. Its functional role is to convert the adjective/adverb 'most' into a standard adverb of manner or degree.