How many words start with US?

10, from 5 letters up to 5. All of them are on this page.

What is the highest scoring word that start with US?

USQUE at 14 points in Scrabble, and USQUE at 16 in Words With Friends, because the two games score the tiles differently.

USAGE, USERS, USHER, USING, USNEA, USQUE, USUAL, USURE, USURP, USURY.

10 of them: USAGE, USERS, USHER, USING, USNEA, USQUE, USUAL, USURE, USURP, USURY.

There are 10 of them. The highest scoring is USQUE at 14 points in Scrabble, and the set averages 6.9.

Most common words first, then the rest A to Z.

The most familiar words on this page and what they mean. Tap any word for its full entry, score and anagrams.

USING noun an act that exploits or victimizes someone (treats them unfairly)
USERS noun form of USER: a person who makes use of a thing
USAGE noun the act of using
USUAL adjective occurring or encountered or experienced or observed frequently or in accordance with regular practice or procedure
USHER noun an official stationed at the entrance of a courtroom or legislative chamber
USURP verb seize and take control without authority and possibly with force
USURY noun an exorbitant or unlawful rate of interest

Definitions from Open English WordNet, CC BY 4.0.

All of them: Word lists.