Reaching extremes, having to depend (5)
I believe the answer is:
hinge
'depend' is the definition.
(I've seen this in another clue)
'reaching extremes having' is the wordplay.
'having' indicates a hidden word.
'HINGE' is hidden within 'reaching extremes'.
'to' acts as a link.
(Other definitions for hinge that I've seen before include "Joint on which things turn" , "door open because of this?" , "hang" , "Joint between door and frame" , "Pivotal point" .)