1. [adj]  previously used or owned by another; "bought a secondhand (or used) car"
2. [adj]  employed in accomplishing something; "the principle of surprise is the most used and misused of all the principles of war"- H.H.Arnold & I.C.Eaker
3. [adj]  of persons; taken advantage of; "after going out of his way to help his friend get the job he felt not appreciated but used"

USED is a 4 letter word that starts with U.