A record that a thing was received. A receipt exists to protect the one who gave.
Anglo-Norman receite, from Medieval Latin recepta (a thing received), from Latin recipere (to receive): re- (back) + capere (to take); a receipt exists to prove that a taking-back actually happened.
A record that a thing was received. The root's taking-back is the point of keeping one: a receipt exists to protect whoever gave, by proving the giving landed.