Entrance used only one day a week, to the vessel? (7)
I believe the answer is:
frigate
'the vessel?' is the definition.
(frigate is a kind of vessel)
'entrance used only one day a week' is the wordplay.
I cannot really see how this works, but
'entrance' could be 'gate' (type of entrance) and 'gate' is located in the answer.
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
This may be the basis of clue (or it may be nonsense).
'to' acts as a link.
Can you help me to learn more?
(Other definitions for frigate that I've seen before include "Warship - seabird" , "Type of warship" , "Naval escort vessel" , "US warship" , "Warship; -- bird" .)