Meaning and Name Origin
Gareth \g(a)-re-th\ as a boys' name is pronounced GARE-eth. It is of Celtic origin, and the meaning of Gareth is "gentle". Sir Gareth, noted for his modesty and bravery, was a knight of King Arthur's Round Table. Literary: the name appeared in the 15th century in Sir Thomas Malory's "Le Morte D'Arthur". It may have been a form of Geraint, or be linked to Welsh gwaraidd meaning "gentle". Gary, which is actually an independent name, is often used as a pet form of Gareth.
Gareth is an uncommonly occurring first name for males. Gareth is an uncommon surname too for both adults and children. (2000 U.S. Census)
Shown below is a comparison of the popularity of Gareth and associated names. Garret, Garry, Garth and Gary (#560 the previous year) are the prominent alternative forms of Gareth (#unlisted) listed in the Top 1000. Usage of these boy names was at its most widespread during 1960-1969 and has become much less since, with the versions Garret, Garry, Garth and Gary becoming less fashionable. (2014 Birth Statistics)