English
retainment
From retain + -ment.
Formed from retain + -ment
Proto-Indo-European *ten- ‘to stretch, extend’
…
Vulgar Latin *retinīre
Middle French retenir ‘to keep’
Anglo-Norman reteiner
Middle English reteinen
English retain
Today it means
noun retention
Language periods are conventional ranges, not dates for this word.
Etymograph / retainment