The word "widow" is for women, while the male version adds "-er" onto it.
I can't think of any other words in English that does this. There's words where male and female have different endings ("actor" versus "actress"), and cases where you specify maleness by putting "male" at the front ("male nurse", "male prostitute", "male geisha"), but nothing where you take an existing word, fail to remove anything, and then add some suffix. Are there any such words?
According to An Easy English Grammar for Beginners (1864):
There are three words in the English language which derive the masculine form from the feminine. These are widower, gander, and drake. Widow, in Old English, is both masculine and feminine, as the word spouse still is ; but, as the word widow came to be used solely of women, the need of some distinction was felt, and er was added for the masculine. The old form for goose was gans or gand. Add the masculine ending er, and we have gander. The old word for duck was and; add the masculine suffix rake, and we have andrake, which is the old form of the word. It was then shortened into drake.
