Returning one weapon left your leader in a sleepy way (8)

'in a sleepy way' is the definition.
I can't tell whether this definition defines the answer.

'returning one weapon left your leader' is the wordplay.
'returning' shows that the letters should be reversed in order.
'one' becomes 'i' (Roman numeral).
'weapon' becomes 'sword' (sword is a kind of weapon).
'leader' says to take the initial letters.
The initial letters of 'left your' is 'ly'.
'i'+'sword'='isword'
'isword' written backwards gives 'drowsi'.
'drowsi'+'ly'='DROWSILY'

Can you help me to learn more?