/ Dictionary / Index P pyrethroid: Meaning and Definition of Find definitions for: py•re•throid Pronunciation: (pī-rē'throid, -reth'roid), [key] — n. Chem. any of several synthetic compounds that are similar to but more persistent than natural pyrethrins. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. pyrethrin pyrethrum Related Content Daily Word Quiz: hale Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language