Yes, us is a Scrabble word!

Noun

1. North American republic containing 50 states - 48 conterminous states in North America plus Alaska in northwest North America and the Hawaiian Islands in the Pacific Ocean; achieved independence in 1776

2. A base containing nitrogen that is found in RNA (but not in DNA) and derived from pyrimidine; pairs with adenine

3. A heavy toxic silvery-white radioactive metallic element; occurs in many isotopes; used for nuclear fuels and nuclear weapons

4. The 21st letter of the Roman alphabet