Origin: Greek prefix anti-
Antiknock has 4 different meanings across 2 categories:
any of various compounds that are added to gasoline to reduce engine knocking
Such a substance, usually tetraethyl lead (also MMT, MTBE and ethanol)
suppressing or eliminating engine knock in combustion engines
"antiknock properties"
"antiknock rating"
Of an additive added to petroleum/gasoline to reduce the occurrence of engine knock.