Sense trend that's developed to show kindly quality (10)
I believe the answer is:
tenderness
'kindly quality' is the definition.
(quality of being tender or kind)
'sense trend that's developed' is the wordplay.
'that's developed' is an anagram indicator.
'sense'+'trend'='sensetrend'
'sensetrend' with letters rearranged gives 'TENDERNESS'.
'to show' acts as a link.
(Other definitions for tenderness that I've seen before include "sore?" , "Gentleness, sensitivity" , "Gentle quality" , "Compassion" , "Heart" .)