Meaning : Make straight.
Synonyms : straighten out
Meaning : Get up from a sitting or slouching position.
Example :
The students straightened when the teacher entered.
Meaning : Put (things or places) in order.
Example :
Tidy up your room!.
Synonyms : clean up, neaten, square away, straighten out, tidy, tidy up
Meaning : Make straight or straighter.
Example :
Straighten this post.
Straighten hair.