Definition of sit-up
(Entry 1 of 2)
: a conditioning exercise performed from a supine position by raising the torso to a sitting position and returning to the original position without using the arms or lifting the feet
sit up
verb
sat up; sitting up; sits up
Definition of sit up (Entry 2 of 2)
1a
: to rise from a lying to a sitting position
b
: to sit with the back erect
2
: to show interest, alertness, or surprise
sit up and take notice
3
: to stay up after the usual time for going to bed
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Merriam-Webster unabridged
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Time Traveler for sit-up
The first known use of sit-up was in the 13th century
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