In the first place; primarily or most importantly; in a foremost manner.
From 'foremost' (first in position or importance) + '-ly' (adverbial suffix). This would theoretically mean 'in a foremost way' or 'as a foremost consideration.'
This word is almost never used—English speakers say 'first and foremost' or 'primarily' instead—showing how '-ly' adverbs don't work the same way on superlatives as they do on regular adjectives.
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