Interval moments back, when lunch may be served? (8)
I believe the answer is:
semitone
'interval' is the definition.
(semitone is a kind of interval)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for semitone that I've seen before include "Small musical interval" , "One twelfth of an octave" , "Small interval between notes" , "Minimum interval in diatonic scale" , "Interval between adjacent keys, on a piano say" .)