buckle down

Collins Concise English Dictionary © HarperCollins Publishers::

buckle down verb

1. (intr, adverb) to apply oneself with determination

WordReference Random House Learner's Dictionary of American English © 2025

buck•le /ˈbʌkəl/   n., v., -led, -ling. 
n. [countable]

1. a piece of metal attached to one end of a belt or strap, used for fastening to the other end of the same strap or to another strap:
   His brass belt buckle flashed in the light.

v. 

2. to fasten with a buckle or buckles: [~ + object]
   Buckle your seat belt.
   [~ + on + object]
   The officer buckled on his pistol.
   [~ + object + on]
   He buckled his pistol on.
3. to bend because of fatigue:
   [no object] Suddenly my knees buckled.
4. to bend, curl, or collapse suddenly because of heat or pressure: [no object]
   When the earthquake hit, several highways buckled.
   [~ + object]
   The intense heat buckled the road.
5. buckle down, [no object] to set to work with strength and determination:
   Just buckle down and practice.
6. buckle under, [no object] to surrender, give way, or yield to another:
   The stubborn worker finally began to buckle under.
7. buckle up, [no object] to fasten one's belt, seat belt, or buckles:
   Please buckle up now; we're about to land.

WordReference Random House Unabridged Dictionary of American English © 2025

buck•le  (buk′əl), n., v., -led, -ling. 
n. 

1. 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.
2. any similar contrivance used for such purposes.
3. Jewelry an ornament of metal, beads, etc., of similar appearance.
4. a bend, bulge, or kink, as in a board or saw blade.

v.t. 

5. to fasten with a buckle or buckles:
   Buckle your seat belt.
6. to shrivel, by applying heat or pressure;
   bend;
   curl.
7. to prepare (oneself ) for action;
   apply (oneself ) vigorously to something.
8. to bend, warp, or cause to give way suddenly, as with heat or pressure.

v.i. 

9. to close or fasten with a buckle:
   Grandmother always wore shoes that buckled.
10. to prepare oneself or apply oneself:
    The student buckled to the lesson.
11. to bend, warp, bulge, or collapse:
    The bridge buckled in the storm.
12. to yield, surrender, or give way to another (often fol. by under):
    She refused to take the medicine, but buckled under when the doctor told her to.
13. buckle down, to set to work with vigor;
    concentrate on one's work:
    He was by nature a daydreamer and found it hard to buckle down.
14. buckle up, to fasten one's belt, seat belt, or buckles:
    She won't start the car until we've all buckled up.

• Latin buc(c)ula cheekpiece (of a helmet), strip of wood, etc., resembling a cheekpiece, equivalent. to bucc(a) cheek + -ula -ule
• Anglo-French bo(u)cle, bucle
• Middle English bocle 1300–50

buck′le•less, adj. 
Synonyms

• 8. sag, bulge, twist; crumple, collapse.