Deck hands in old Royal Navy attending (8)
I believe the answer is:
ornament
'deck' is the definition.
(I know that ornament is a type of deck)
'hands in old royal navy attending' is the wordplay.
'hands' becomes 'men' (synonyms).
'in' is an insertion indicator.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'royal navy' becomes 'RN' (abbreviation for Royal Navy).
'attending' becomes 'at' (I've seen this in other clues).
'o'+'rn'+'at'='ornat'
'men' going within 'ornat' is 'ORNAMENT'.
(Other definitions for ornament that I've seen before include "Something decorative" , "Turn" , "small decorative object" , "accessory" , "Decorate" .)