most

The word 'most' is the superlative degree of both 'much' and 'many' in Modern English, and it also serves as the standard way to form analytic superlatives ('most beautiful,' 'most interesting').‍​‌​‍​‌​‍​‍​‌​‌​‌​‌​‌​‌​‌​‍​‍​‍​‌​‍​‍​‍​‍​‍​‌​‌​‍​‍​‌​‍​‌​‍​‍​‍ Despite this central grammatical role, 'most' is etymologically unrelated to either of the words whose paradigm it completes — a phenomenon linguists call suppletion.

Old English 'māst' (greatest, largest, most) was the superlative corresponding to the comparative 'māra' (more, greater). Both forms descend from Proto-Germanic *maistaz (superlative) and *maizô (comparative), built on a root *mais- that can be traced to PIE *mē- (big, great). The cognates are consistent across Germanic: Gothic 'maists,' Old Norse 'mestr,' Old High German 'meist' (Modern German 'meist'), Old Saxon 'mēst,' and Dutch 'meest.'

The PIE root *mē- also produced Latin 'magis' (more, rather) — the source of 'master,' through Latin 'magister' — and the suffix seen in Latin 'maximus' (greatest), from *mag-simos. But *mē- is not the same root as *meǵh₂- (the source of 'much,' 'mega,' 'magnus'). Despite their similar meanings, these are considered two distinct PIE roots by most etymologists. The confusion is understandable: both meant 'big/great,' both produced comparison words, and they may ultimately be related at a pre-PIE level. But within the reconstructed PIE system, they are kept apart.

The suppletive paradigm in English is remarkable. The positive degree is supplied by two words: 'much' (from PIE *meǵh₂-) for uncountable nouns and 'many' (from Proto-Germanic *managaz) for countable nouns. The comparative is 'more' (from PIE *mē- via Proto-Germanic *maizô). The superlative is 'most' (from PIE *mē- via Proto-Germanic *maistaz). Three different etymological sources — *meǵh₂-, *managaz, and *mē- — are pressed into service as a single grammatical paradigm. Speakers treat 'much/many — more — most' as a unified system, completely unaware that its components have different ancestries.

This kind of suppletion occurs elsewhere in English: 'good/better/best' (where 'better' and 'best' come from a different root than 'good'), 'bad/worse/worst,' and 'go/went' (where 'went' was originally the past tense of 'wend'). Suppletion tends to survive in the most frequently used words, precisely because they are learned as whole units rather than derived by rule.

Beyond its comparative function, 'most' developed the ability to form analytic superlatives in Middle English. Where Old English and early Middle English used the suffix '-est' almost exclusively ('fairest,' 'wisest'), later Middle English began using 'most' with longer adjectives ('most beautiful,' 'most excellent'). By the 16th century, the modern rule of thumb was emerging: '-est' for short adjectives, 'most' for longer ones, though the boundary remains fuzzy ('commonest' vs. 'most common' are both acceptable).

The word also functions as a noun and pronoun ('most of them'), an adverb ('most likely'), and appears in compounds: 'almost' (Old English 'eal māst,' literally 'nearly the greatest amount'), 'foremost' (where '-most' was reinterpreted as the superlative suffix, though 'foremost' actually comes from Old English 'formest,' a double superlative), 'utmost' (from Old English 'ūtemest,' outermost), 'innermost,' 'uppermost,' and 'nethermost.' In these compounds, '-most' functions as a productive suffix meaning 'to the greatest degree,' detached from its origins as a standalone superlative.

The history of 'most' thus reveals two things about English: the language tolerates — even depends upon — suppletive paradigms where different roots unite under one grammatical function, and it recycles its most common words into new structural roles, turning a superlative pronoun into a grammatical particle for forming superlative adjectives.