Someone who intimidates us, making us shrink back? (5)
I believe the answer is:
cower
'shrink back?' is the definition.
'someone who' is the wordplay.
'someone' becomes 'cow' (cow is a kind of someone).
'who' becomes 'er' (I can't justify this - if you can you should give a lot more credence to this answer).
'cow'+'er'='COWER'
'intimidates us making us' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
(Other definitions for cower that I've seen before include "Grovel in fear" , "Show abject fear" , "Bend in fear" , "Cringe, grovel" , "Crouch in fear" .)