In microwave, reheats a little nightcap: nobleman's losing head (5)
I believe the answer is:
nukes
'in microwave reheats a' is the definition.
I can't tell whether this defines the answer.
'little nightcap nobleman's losing head' is the wordplay.
'little' says to take the initial letters.
'nobleman's' becomes 'duke's' (duke is a kind of nobleman).
'losing head' means to remove the first letter.
The initial letter of 'nightcap' is 'n'.
'dukes' with its initial letter taken away is 'ukes'.
'n'+'ukes'='NUKES'
Can you help me to learn more?
(Another definition for nukes that I've seen is " Destructive weapons".)