Ryan Lochte -- I'm Trademarking My Dumb Catchphrase ... JEAH!!!

Ryan Lochte's annoying catchphrase "Jeah!" is a friggin' GOLD MINE -- at least that's what the swimmer believes ... because he just filed docs to lock up a trademark for the made-up word.

According to the trademark docs, Ryan wants to use the word on sunglasses, workout DVDs, gift cards, mugs, drinking glasses, trading cards, calendars, posters, swimsuits, swim caps, sports hats, and water bottles.

In fact, Lochte's already getting the party started on his website -- selling "Jeah"-themed tees, hats, and sunglasses.

According to a 2009 interview, Ryan got the phrase from rapper Young Jeezy, who uses a similar word "Chea!" in his songs. Ryan says he changed it a little to "Jeah!" ... and says it means something "good." (skip to 1:00)