PEA Originally the word was “pease,” and it was singular.The sound on the end was reanalyzed as a plural ‘s’ marker.
CHERRY The same thing happened to “cherise” or “cheris,” which came from Old French “cherise” and was reanalyzed as a plural. So the singular “cherry” was born.
APRON Originally “napron” often enough as “an apron” that by the 1600s the “n” was dropped.
UMPIRE Umpire lost its ‘n’ from the same sort of confusion. Orinally nompere, the n-less form won out.
NEWT A newt was originally an “ewt” - with “an” thus it became the “newt.”
NICKNAME The ‘n’ also traveled over from the “an” to stick to “nickname,” which was originally “ekename,” meaning “added name.”
ALLIGATOR Alligator came to English from the Spanish explorers who first encountered “el lagarto” (lizard) in the New World.