=Singular.= = Plural.= =Plural.=
penny, pennies (a number.) pence (a sum.)
pea, peas (a number.) pease (a quantity.)
brother, brothers (same family.) brethren (same society.)
die, dies (for stamping.) dice (for gaming.)
cloth, cloths (kinds of cloth.) clothes (garments.)
index, indexes (to a book.) indices (in algebra.)
genius, geniuses (men of talent.) genii (spirits.)