Maintenance
Middle English (in the sense ‘aiding a party in a legal action without lawful cause’): from Old French, from maintenir (see maintain).
wiktionary
From Middle English mayntenaunce, from Old French maintenance, from maintenir, from Latin manus tenēre(“to hold in the hand”). Surface analysis is maintain + -ance.
Note that maintain has undergone a sound and spelling change, hence is spelt with -tain-, rather than the -ten- still found in maintenance.
etymonline
maintenance (n.)
mid-14c., maintenaunce, "wrongful interference in others' lawsuits by a lord or his followers," from Old French maintenance "upkeep; shelter, protection," from maintenir "to keep, sustain; persevere in" (see maintain). Meaning "action of upholding or keeping in good order" is from early 15c. That of "action of providing a person with the necessities of life," also "financial provision or support, that which maintains or supports" is from late 14c.
