Question: what are words with double letters?
Answer: There is a much larger number of double letter words when you add a letter to make a 4 letter word, such as ball, been, beer, beet, beep, bell, boom, boot, book, bull, butt, call, cell, coon, dell, doll, door, doom, fall, fell, feel, feet, foot, food, fool, fuss, full, gull, gall, hall, hell, heed, heel, hill, hull, ...