Sailor’s complaint, sick at first with waves (6)
I believe the answer is:
scurvy
'sailor's complaint' is the definition.
'scurvy' can be an answer for 'complaint' (scurvy is a kind of health problem). I'm unsure of the 'sailor's' bit.
'sick at first with waves' is the wordplay.
'at first' says to take the initial letters.
'with waves' becomes 'curvy'.
The initial letter of 'sick' is 's'.
's'+'curvy'='SCURVY'
Can you help me to learn more?
(Other definitions for scurvy that I've seen before include "an old naval problem" , "Result of vitamin C deficiency" , "problem for many a sailor?" , "Condition caused by lack of vitamin C" , "Sailors' old disease" .)