To straighten s.t.; to align s.t. (in a straight line).
Like iron that is crooked; it is straightened so that it will be straight.
I asked her to straighten the arm of my child.
Those quarreling people don’t want to be straightened out.
The posts of his house cannot be (put in a) straight (row with others) because they are crooked.
When you plant coconuts, align (make a straight line) them with this stick.