(idiomatic) (originally) by the authority or power of; (now) because of; on the grounds of; by reason of.

(idiomatic) Describing things are handled more efficiently as a group, rather than individually.

Alone; without assistance or help from others. / Alone, without another's immediate company / (rare) Used other than figuratively or idiomatically: see by, oneself.

Alternative spelling of by the by

(logic) The indirect verification or falsification of a statement by the verification or falsification of each of the finite number of cases which arise therefrom.

plural of proof by exhaustion

(idiomatic) to do something exactly, precisely, or in a formulaic way.

plural of clue-by-four

(informal, humorous, figuratively) A notional weapon used to knock sense into the clueless.

Alternative form of clue-by-four