1530s, "a release from confinement," from enlarge in the secondary Middle English sense "release a prisoner" (mid-15c.) + -ment. Meaning "act of increasing in size" is from 1560s. Photographic sense "picture of a larger size than the negative from which it was made" is from 1866.
enjoyable
enjoyment
enkindle
enlace
enlarge
enlargement
enlighten
enlightened
enlightenment
enlist
enlistment