Leaving when there's a summons to lunch, round about one (5)
I believe the answer is:
going
'leaving' is the definition.
(synonyms)
'there's a summons to lunch round about one' is the wordplay.
I cannot really see how this works, but
'there's' could be 'n' (I've seen this in other clues) and 'n' is found within the answer.
'round' could be 'o' (o is a circular letter) and 'o' is found in the answer.
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
This explanation may well be incorrect...
'when' is the link.
Can you help me to learn more?
(Other definitions for going that I've seen before include "Disappearing" , "Surface condition (that may get tough!)" , "Departure; current (rate)" , "fading" , "Running; leaving" .)