Port thus knocked back by nurse (6)
I believe the answer is:
ostend
'port' is the definition.
(I know that Ostend is a port)
'thus knocked back by nurse' is the wordplay.
'thus' becomes 'so' (synonyms).
'knocked back' is a reversal indicator.
'by' says to put letters next to each other.
'nurse' becomes 'tend' (tend can mean to nurse or look after).
'so' written backwards gives 'os'.
'os'+'tend'='OSTEND'
(Other definitions for ostend that I've seen before include "European port" , "Port - doesn't (anag)" , "Channel port" , "Port in Belgium" , "somewhere in Europe" .)