Melancholy face when the sergeant-major comes in (6)
I believe the answer is:
dismal
'melancholy' is the definition.
(I've seen this in another clue)
'face when the sergeant-major comes in' is the wordplay.
'face when' becomes 'dial' (face of a clock. I am not sure about the 'when' bit.).
'the sergeant major' becomes 'SM' (abbreviation for sergeant major).
'comes in' means one lot of letters goes inside another.
'dial' placed around 'sm' is 'DISMAL'.
Can you help me to learn more?
(Other definitions for dismal that I've seen before include "Lugubrious" , "Wretched" , "describes economic science" , "Dull and dreary" , "Miserable" .)