UM
Worth 4 points before any premium square, and the 34th highest-scoring of 96 — tied with 18 others.
UM extends into 11 three-letter words, which is the 41st most extendable of 96 — tied with 3 others. That is the number worth memorising: a two-letter word is a place to put tiles, but a well-hooked one is a place to put them where the board stays open.
Every hook
- B→BUM
- C→CUM
- G→GUM
- H→HUM
- L→LUM
- M→MUM
- R→RUM
- S→SUM
- Y→YUM
- M→UMM
- P→UMP
Not all of them are equally reachable, which a bare count of 11 hides. UM hooks on 10 distinct letters, and the ones you are likeliest to be holding are R (36% of opening racks), L (26% of opening racks) and S (26% of opening racks). The rarest is P, at 14%.
How often you can actually play it
Out of an opening rack, 3.06% of the time you hold the letters for UM outright, the 12th least likely of 96 — tied with 4 others. Counting a blank as whichever letter is missing lifts that to 7.41%, though spending one of the two blanks on a two-letter word is rarely the play. Exact hypergeometrics over the 100-tile bag, not a simulation.
It reverses
UM backwards is MU, which is also good. That is how most of this list is actually learned — 46 of the 96 come in reversible pairs, so knowing one gets you the other free.