Voluntary service based on an individuals' desire to serve a cause. (noun)
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Use "enlistment" in a sentence
"For starters, how about free tuition & books at any state university in exchange for a one term enlistment?"
"I mean, with wars going in two nations most Americans can't find on a map and thousands dying or coming home in pieces after having their deployments extended over and over again (while at the same time being prevented from leaving the service when their enlistment is up), who wouldn't rather obsesses over some missing white woman or other, or bemoan the steroidal state of professional baseball?"
"Our legislation encourages more young Americans to serve in the military by allowing the Defense Department to create a new, shorter-term enlistment option."