enlist

from The American Heritage® Dictionary of the English Language, 5th Edition.

• intransitive verb To engage (persons or a person) for service in the armed forces.
• intransitive verb To engage the support or cooperation of.
• intransitive verb To enter the armed forces.
• intransitive verb To participate actively in a cause or enterprise.

from The Century Dictionary.

• To enter, as a name on a list; enroll; register.
• To engage for public service, especially military or naval service, by enrolling after mutual agreement: as, to enlist men for the army.
• To unite firmly to a cause; employ in advancing some interest; engage the services of: as, to enlist one's sympathies in the cause of charity.
• Synonyms and Enroll, etc. See record, v.
• To engage in public service, especially military service, by subscribing articles or enrolling one's name; specifically, to engage in such service voluntarily.
• To enter heartily into a cause, with devotion to its interests.

from the GNU version of the Collaborative International Dictionary of English.

• intransitive verb To enroll and bind one's self for military or naval service
• intransitive verb To enter heartily into a cause, as if enrolled.
• transitive verb To enter on a list; to enroll; to register.
• transitive verb To engage for military or naval service, the name being entered on a list or register.
• transitive verb To secure the support and aid of; to employ in advancing interest.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb intransitive To join a cause or organization, especially military service.
• verb transitive To recruit the aid or membership of others.
• verb To secure, to obtain.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb hire for work or assistance
• verb engage somebody to enter the army
• verb join the military