Some naval craft subscriptions (4)
I believe the answer is:
subs
'some naval craft subscriptions' is the definition.
Although both the answer and definition are plural nouns, I cannot see how they can define each other.
'craft subscriptions' is the wordplay.
'craft' becomes 'sub' (sub is a kind of craft).
'subscriptions' becomes 's' (this could be a standard abbreviation of which I'm unaware).
'sub'+'s'='SUBS'
Can you help me to learn more?
(Other definitions for subs that I've seen before include "Advance payments" , "Underwater vessels (abbr)" , "Players in reserve" , "vehicles" , "Club members' payments" .)