antiknock

nouns

any of various compounds that are added to gasoline to reduce engine knocking
antiknock
is a type of (narrower)
(chemistry) a substance formed by chemical union of two or more elements or ingredients in definite proportion by weight
chemical compound, compound

adjectives

suppressing or eliminating engine knock in combustion engines
"antiknock properties"; "antiknock rating"
antiknock, antiknocking