Friday’s child? That’s a thrill! (7)
I believe the answer is:
frisson
'a thrill' is the definition.
('frisson' can be a synonym of 'thrill')
'friday's child?' is the wordplay.
'friday's' becomes 'fris' ('Fri' can be a synonym of 'friday').
'child?' becomes 'son' (son is a kind of child).
'fris'+'son'='FRISSON'
'that's' is the link.
(Other definitions for frisson that I've seen before include "Emotional thrill" , "A shudder or thrill" , "Strong feeling of excitement, thrill" , "Shiver of excitement" , "Kick" .)