Rocked to sleep, I will drop love letter (7)
I believe the answer is:
epistle
'letter' is the definition.
(I know that epistle is a type of letter)
'rocked to sleep i will drop love' is the wordplay.
'rocked' indicates an anagram.
'will drop' is a deletion indicator.
'love' becomes 'o' (love means zero in tennis).
'to'+'sleep'+'i'='tosleepi'
'tosleepi' with 'o' taken out is 'tsleepi'.
'tsleepi' is an anagram of 'EPISTLE'.
(Other definitions for epistle that I've seen before include "Maybe Paul's" , "Missive; letter" , "a for instance" , "Specially long and formal letter" , "Letter, in the Bible perhaps" .)