Measures of resistance in the service of the monarch? (4)
I believe the answer is:
ohms
'measures of resistance' is the definition.
(I've seen this before)
'in the service of the monarch?' is the wordplay.
'in the' means one lot of letters goes inside another.
'service of' becomes 'os' (I can't explain this - if you can you should give a lot more credence to this answer).
'the monarch?' becomes 'hm' (short for Her Majesty).
'os' placed around 'hm' is 'OHMS'.
Can you help me to learn more?
(Other definitions for ohms that I've seen before include "working for the monarchy?" , "Frank on official post" , "measures of resistance" , "Frank marking" , "lab units" .)