Simple past tense and past participle of unbuckle.(verb)
Wiktionary.org : Text is available under the Creative Commons Attribution-ShareAlike License
Use "unbuckled" in a sentence
"In a press conference Monday, Headley said the airlines are not "rolling in money" but since they've "unbuckled" some of their services, they've freed up cash flow."
"Me: So, imagine you're in the SpaceShipTwo, you've gotten to the point where you're in microgravity, you're unbuckled, what's the first thing you would do?"
"He pushed himself between her legs and unbuckled his belt, unzipped his pants."