assistance

Middle English assistence, assistance, borrowed from Anglo-French, borrowed from Medieval Latin assistentia "presence, participation, guidance," going back to Late Latin, "aid," noun derivative of Latin assistent-, assistens, present participle of assistere "to take up a position near, stand by, stand by as a supporter or advocate" — more at assist entry 1

Note: In the case of both this word and assistant Modern English has chosen the French form with -a- in the suffix rather than Latin -e-.