intransitive. To unite or enter into alliance for a common purpose or mutual benefit. Chiefly with with.

intransitive (for reflexive). To enter into an alliance or league; to ally oneself.

transitive (Scots Law.) Hence, to fence a band: to make a league (Latin ferīre fœdus). Obsolete. rare.

intransitive. To form an alliance; to ally oneself with. rare.

Phr. to enter league: to make a covenant or alliance; to interleague, v. Obsolete.

intransitive (for reflexive). Of persons or states: To enter into a league, ally or league oneself (with.)

intransitive. To join in or form a league or alliance; to band together. Also to league against in indirect passive.