Ages of sailing ships halved (4)
I believe the answer is:
eons
'ages' is the definition.
(I know this)
'sailing ships halved' is the wordplay.
'sailing ships' becomes 'galleons' (galleon is a kind of sailing ship).
'halved' means to take half the letters.
'galleons' with half the letters taken is 'EONS'.
'of' is the link.
(Other definitions for eons that I've seen before include "Vast ages" , "Long periods of time - noes have it" , "Endless periods" , "Very long periods (US)" , "Times" .)