What It Scores
ONIUM is a valid word in the tournament list this site uses. Tile values only, before any premium square: 7 in Scrabble and 8 in Words With Friends. The letters break down as O1 N1 I1 U1 M3.
Words Made From The Letters In ONIUM
24 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 (3)
3 letter words (8)
2 letter words (13)
Longer Words Containing ONIUM
ONIUM 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.