What It Scores
BILLY is a valid word in the tournament list this site uses. Tile values only, before any premium square: 10 in Scrabble and 11 in Words With Friends. The letters break down as B3 I1 L1 L1 Y4.
Words Made From The Letters In BILLY
9 shorter words come out of these tiles. On a board that matters more than the long play, because a short word on a premium square often beats a long one on plain squares.
4 letter words (4)
3 letter words (2)
2 letter words (3)
Longer Words Containing BILLY
BILLY appears inside each of these, which is what makes it worth knowing as a hook.
Next: the Word Unscrambler for any letters at all. Full entry and definition at Merriam-Webster.