buckle

1 buckle /ˈbʌkəl/ noun
plural buckles
1 buckle
/ˈbʌkəl/
noun
plural buckles
Britannica Dictionary definition of BUCKLE
[count]
: a metal or plastic device that is attached to one end of a belt or strap and that is used to connect it to the other end — see picture at shoe
2 buckle /ˈbʌkəl/ verb
buckles; buckled; buckling
2 buckle
/ˈbʌkəl/
verb
buckles; buckled; buckling
Britannica Dictionary definition of BUCKLE
1 
[+ object]
a  : to fasten (something, such as a belt) with a buckle
b  : to attach (something) with a buckle
2 
a  [no object] : to bend or collapse from pressure, heat, etc.
— often used figuratively
b  [+ object] : to cause (something) to bend or collapse

buckle down

[phrasal verb] informal
: to start to work hard

buckle up

[phrasal verb] US
: to fasten your seat belt in a car or other vehicle