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Longman Dictionary of Contemporary English
military service
noun
EXAMPLES FROM CORPUS
▪ Armed forces: No standing army since 1868; citizens under 60 liable to military service in emergency.
▪ Franken also avoided military service with student deferments while at Harvard and, ultimately, a high lottery number.
▪ He had one dose of diphtheria vaccine during military service in 1970.
▪ It is true that the archbishop's lands were already overstocked with knights in relation to the military service due from them.
▪ Simply comparing the incomes of those experiencing military service with those who did not will not do.
▪ They will consider introducing exemptions from or alternatives to military service. 29.
▪ Why had Hencke been exempted from military service?
Wiktionary
military service

n. Service in an army or other military organisation, whether as a chosen job or as a result of an involuntary draft (conscription).

WordNet
military service
  1. n. a force that is a branch of the armed forces [syn: armed service, service]

  2. land tenure by service in the lord's army

Wikipedia
Military service

Military service is service by an individual or group in an army or other militia, whether as a chosen job or as a result of an involuntary draft ( conscription). Some nations (e.g., Mexico) require a specific amount of military service from every citizen (except for special cases, such as physical or mental disorders or religious beliefs, and most countries that have conscription only conscript men). A nation with a fully volunteer military does not normally require mandatory military service from its citizens, unless it is faced with a recruitment crisis during a time of war.