Serviceman in receding tide finds protection (5)
I believe the answer is:
aegis
'protection' is the definition.
(synonyms)
'serviceman in receding tide' is the wordplay.
'serviceman' becomes 'gi' (I've seen this in other clues).
'in' means one lot of letters goes inside another.
'receding' says the letters should be written backwards.
'tide' becomes 'sea' (I have seen 'The tide' mean 'sea' so perhaps 'tide' could also mean 'sea').
'sea' in reverse letter order is 'aes'.
'gi' going within 'aes' is 'AEGIS'.
'finds' acts as a link.
(Other definitions for aegis that I've seen before include "strong defence" , "Protection - guardianship" , "Backing or support" , "Protection or support" , "Kindly protection" .)