Round container Crusoe finally dropped in sea (5)
I believe the answer is:
ocean
'sea' is the definition.
('ocean' can be a synonym of 'sea')
'round container crusoe finally dropped' is the wordplay.
'round' becomes 'o' (round can mean a round object).
'container' means to remove the middle letters (I've seen 'container of' mean this).
'finally dropped' becomes 'an' (I can't explain this - if you can you should believe this answer much more).
'crusoe' with its centre taken out is 'ce'.
'o'+'ce'+'an'='OCEAN'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for ocean that I've seen before include "The deep" , "Large expanse of sea" , "One of the Seven Seas" , "Large stretch of sea" , "Vast quantity of liquid" .)