Real Dictionary

buckle
countable noun: A buckle is a piece of metal or plastic attached to one end of a belt or strap, which is used to fasten it.
verb: If an object buckles or if something buckles it, it becomes bent as a result of very great heat or force.
verb: If your legs or knees buckle, they bend because they have become very weak or tired.
verb: When you buckle a belt or strap, you fasten it.

buckle in American English
intransitive verb: to close or fasten with a buckle
noun: a clasp consisting of a rectangular or curved rim with one or more movable tongues, fixed to one end of a belt or strap, used for fastening to the other end of the same strap or to another strap
transitive verb: to fasten with a buckle or buckles

buckle in American English 1
a clasp on one end of a strap or belt for fastening the other end in place
to be fastened or joined by a buckle
to fasten or join with a buckle

buckle in American English 2
a distortion caused by buckling; bend, bulge, kink, etc.
to bend, warp, or crumple, as under pressure or in intense heat

buckle in British English
noun: a clasp for fastening together two loose ends, esp of a belt or strap, usually consisting of a frame with an attached movable prong
verb: to fasten or be fastened with a buckle