Saddle and take one's leave about midnight (5)
I believe the answer is:
ridge
'saddle' is the definition.
(I've seen this before)
'take one's leave about midnight' is the wordplay.
'take one's leave' becomes 'ride' (both can mean to leave a place).
'about' indicates putting letters inside.
'midnight' becomes 'g' (the middle letter in 'night').
'ride' enclosing 'g' is 'RIDGE'.
'and' is the link.
(Other definitions for ridge that I've seen before include "Narrow elevated strip" , "Bump between furrows" , "Line where two upward sloping surfaces meet" , "Narrow raised band on a surface" , "roof-tree" .)