suppletory
adjective
sup·ple·to·ry sə-ˈplē-tə-rē 
ˈsə-plə-ˌtȯr-ē
ˈsə-plə-ˌtȯr-ē : supplying deficiencies : supplementary
rules suppletory to the contract
Word History
Etymology
borrowed from New Latin supplētōrius, from Latin supplēre "to fill up, complete, raise to its full complement" + -tōrius, deverbal adjective suffix, originally forming derivatives from agent nouns ending in -tōr-, -tor — more at supply entry 2
First Known Use
circa 1631, in the meaning defined above