Leaves uniform during service etc at sea (7)
I believe the answer is:
'leaves' is the definition.
(I know that lettuce is a type of leaf vegetable)
'uniform during service etc at sea' is the wordplay.
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
'during' is an insertion indicator.
'service' becomes 'let' (type of tennis serve).
'at sea' is an anagram indicator.
'etc' anagrammed gives '[etc]'.
'u' inserted inside 'lettce' is 'LETTUCE'.
(Other definitions for lettuce that I've seen before include "Salad leaves" , "eg Webbs wonder" , "Part of a BLT" , "E.g. cos" , "Plant with broad crisp leaves used in salads" .)