Meaning of “buckle” - Learner’s Dictionary

buckle

verb uk us /ˈbʌkl/
FASTEN [ I, T ]

to fasten a belt or strap with a buckle

BEND [ I, T ]

to bend, or to make something bend because of too much weight, heat, etc:

His legs buckled as he reached the finishing line.
SUFFER [ I ]

to suffer and stop working effectively because of too many problems or too much work

(Definition of “buckle verb” from the Cambridge Learner’s Dictionary © Cambridge University Press)