com·ple·men·ta·tion (kŏmˌplə-mən-tāˈshən, -mĕn-)

1. Functional interaction between two defective viruses permitting replication under conditions inhibitory to the single virus.
2. Interaction between two genetic units, one or both of which are defective, permitting the organism containing these units to function normally, whereas it could not do so if one unit were absent.