A prefix, originally the same word as by
; [1913 Webster
"It is joined with certain substantives, and a few adjectives, to form verbs; as, bedew, befriend, benight, besot; belate (to make late); belittle (to make little). It also occurs in certain nouns, adverbs, and prepositions, often with something of the force of the preposition by, or about; as, belief (believe), behalf, bequest (bequeath); because, before, beneath, beside, between.
In some words the original force of be is obscured or lost; as, in become, begin, behave, behoove, belong."