intransitive (for reflexive) in same sense.

intransitive. Scottish. To set to work; to begin or resume doing something, esp. energetically or enthusiastically; to turn one's attention or direct…

to buckle ˈto: to set to work, apply oneself vigorously. Also to buckle down (to) (originally U.S.).

Nautical. To sail away with the yards squared. Also figurative, to take a new course; to get moving; to put oneself into shape; to make ready.

transitive. slang (originally U.S.).to get it on. To embark on an activity, to get going; to get into full swing; esp. to act or perform music with…