Relatives during gentle run having a laugh (6)
I believe the answer is:
joking
'having a laugh' is the definition.
I can't tell whether this definition defines the answer.
'relatives during gentle run' is the wordplay.
'relatives' becomes 'kin' (kin can mean relatives or family).
'during' indicates putting letters inside.
'gentle run' becomes 'jog' (jogging is a kind of running. I am not sure about the 'gentle' bit.).
'kin' put within 'jog' is 'JOKING'.
Can you help me to learn more?
(Other definitions for joking that I've seen before include "funny" , "Not serious" , "Kidding" , "Jesting, being humorous" , "Making quips" .)