a. 1. Supplying, or tending to supply, a deficiency; fully completing. “Complemental ceremony.” Prynne. [ 1913 Webster ]

2. Complimentary; courteous. [ Obs. ] Shak. [ 1913 Webster ]

Complemental air (Physiol.), the air (averaging 100 cubic inches) which can be drawn into the lungs in addition to the tidal air, by the deepest possible inspiration. --
Complemental males (Zool.), peculiar small males living parasitically on the ordinary hermaphrodite individuals of certain barnacles. [ 1913 Webster ]