To us, possibly, it's an unsettling thing to do (4)
I believe the answer is:
oust
'an unsettling thing to do' is the definition.
I can't tell whether this definition defines the answer.
'to us possibly' is the wordplay.
'possibly' indicates an anagram.
'to'+'us'='tous'
'tous' anagrammed gives 'OUST'.
'it's' acts as a link.
Can you help me to learn more?
(Other definitions for oust that I've seen before include "Force out; supplant" , "Get rid of" , "Unseat" , "Remove from a position of power" , "Extract" .)