To put forth the needed effort; to focus; become serious; apply oneself (e.g. to work or study).(verb)
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Use "buckle down" in a sentence
"We know that global competition-not to mention any genuine commitment to the values of equal opportunity and upward mobility-requires us to revamp our educational system from top to bottom, replenish our teaching corps, buckle down on math and science instruction, and rescue inner-city kids from illiteracy."
"You may think I make light of it - being kidnapped and pressed into sea-slavery, but if I've learned anything it's that when you have no choice, you must just buckle down to misfortune … and wait."