a poisonous European weed of the carrot family that resembles parsley and is naturalized in the northern U.S. and southern Canada

Pronunciation:
foolz PARS-lee

In a sentence:
Eager to open his mind and gain a new spirituality, Evan went looking for Jimson Weed and found fool’s parsley and a middle-aged divorcee named Sandra instead. 

In a different sentence:
Gina was reluctant to try her fiance’s mother’s “parsley tart,” believing (correctly) that it was probably made with large quantities of fool’s parsley, and would probably kill her—or at least significantly delay the wedding.