Depart to cross several large expanses of water, though it could strain the body (7)
I believe the answer is:
disease
'strain the body' is the definition.
The definition and answer can be both states of affairs as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'depart to cross several large expanses of water though it' is the wordplay.
I cannot really see how this works, but
'expanses' could be 'seas' (I've seen this in another clue) and 'seas' is found in the answer.
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found in the answer.
The remaining letters 'di' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'could' acts as a link.
Can you help me to learn more?
(Other definitions for disease that I've seen before include "Ailment, malady" , "affection" , "Seaside (anag) -- ailment" , "Sickness" , "Contagion" .)