rather (adv.)

Old English hraþor "more quickly, earlier, sooner," also "more readily," comparative of hraþe, hræþe "quickly, hastily, promptly, readily, immediately," which is related to hræð "quick, nimble, prompt, ready," from Proto-Germanic *khratha- (source also of Old Norse hraðr, Old High German hrad), from PIE *kret- "to shake." The base form rathe was obsolete by 18c. except in poetry (Tennyson); superlative rathest fell from use by 17c. Meaning "more willingly" is recorded from c. 1300; sense of "more truly" is attested from late 14c.

The rather lambes bene starved with cold
[Spenser, "The Shepheardes Calender" (Februarie), 1579]

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Definitions of rather from WordNet

rather (adv.)
on the contrary; "he didn't call; rather (or instead), he wrote her a letter";
rather than disappoint the children, he did two quick tricks before he left
Synonyms: instead
rather (adv.)
to some (great or small) extent;
the party was rather nice
it was rather cold
I rather regret that I cannot attend
He's rather good at playing the cello
the knife is rather dull
Synonyms: kind of / kinda / sort of
rather (adv.)
more readily or willingly;
I'd rather be in Philadelphia
Synonyms: preferably / sooner
rather (adv.)
to a degree (not used with a negative);
Synonyms: quite