pīˈrēthrə̇n also -reth- noun
( -s )
Etymology: International Scientific Vocabulary pyrethr- (from New Latin Pyrethrum ) + -in; originally formed as French pyréthrine
: either of two oily liquid esters C 21 H 28 O 3rb and C 22 H 28 O 5 of pyrethrolone having high insecticidal properties and occurring especially in pyrethrum flowers — called also respectively pyrethrin I, pyrethrin II