complement protein

This term refers to a specific group of proteins within the innate immune system. It is used primarily in medical, biological, and immunological contexts to describe the biochemical cascade that "complements" the ability of antibodies to clear pathogens.

Because this is a technical scientific term, it is almost exclusively used in formal academic or clinical registers. It should not be confused with the general word "complement" (meaning something that completes) or "compliment" (an expression of praise).