What It Scores
PSI is a valid word in the tournament list this site uses. Tile values only, before any premium square: 5 in Scrabble and 6 in Words With Friends. The letters break down as P3 S1 I1.
Anagrams of PSI (2)
Same letters, different order. Any of these plays the same tiles for the same score.
Words Made From The Letters In PSI
3 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.
2 letter words (3)
Longer Words Containing PSI
PSI appears inside each of these, which is what makes it worth knowing as a hook.
Next: the Word Unscrambler for any letters at all, and the two and three letter lists. Full entry and definition at Merriam-Webster.