Meaning

verb require as useful, just, or proper

noun a condition requiring relief

adverb in such a manner as could not be otherwise

originFrom Middle English nedes (“of necessity, necessarily; inevitably, unavoidably”) [and other forms], from Old English nēdes, nīedes (“of necessity; not willingly”), from nīed + -es (suffix forming adverbs from nouns). The English word is equivalent to need + -'s (possessive marker) and hence to need + -s (suffix forming adverbs).

Etymology from Wiktionary, CC BY-SA 3.0