3 letter words with IO

Our dictionary holds 4 3 letter words with io, all exactly 3 letters long. The highest-scoring of them is BIO, worth 5 points in Scrabble.

More of these words begin with I than any other letter — 2 of them, about 50% of the list.

3 appear in the 20,000 most common English words (75%), including bio, ion, ios; the remaining 1 are rarer finds that still count as valid plays.