The name Dex is a boy's name meaning "dyer; right-handed". Dex and is often added to lists like Nicknames for Boys and discussed in our forums with posts like "Generation CAF w/* England & Wales top 500 2017".
From the experts:
Dex, the nickname for Dexter that is sometimes used on its own, has lots of energy and dynamism. It was chosen by comedian Dana Carvey for his now grown son. With the growing popularity of Dexter, we may be seeing more of Dex.
There are no less than three video game characters named Dex, and the leading male figure in the movie One Day is known by his nickname Dex. Way back in TV's Dynasty era, there was a character redundantly named Dex Dexter.