alike (adj.)

"like one another, very similar," c. 1300, aliche, ylike, ilike, from Old English anlig, onlic "similar, resembling;" from Old English an, on (see a- (1) + like (adj.), which is related to Old English lic "body, corpse."

The notion is "having a corresponding form (body)." The more usual Germanic compound is represented by Old English gelic, from Proto-Germanic *galikam "associated form" (source also of Old Frisian gelik, Dutch gelijk, German gleich, Gothic galeiks, Old Norse glikr). As an adverb, late Old English onlice, gelice.

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Definitions of alike from WordNet
alike (adv.)
parents and teachers alike demanded reforms
Synonyms: likewise
alike (adv.)
in a like manner;
they walk alike
alike (adj.)
having the same or similar characteristics;
friends are generally alike in background and taste
they looked utterly alike
all politicians are alike
Synonyms: similar / like