Turning out to grab handkerchief? There's gratitude! (5,3)
I believe the answer is:
thank you
'gratitude' is the definition.
(I know that Thank you is a type of gratitude)
'turning out to grab handkerchief?' is the wordplay.
'turning' indicates an anagram.
'to grab' means one lot of letters goes inside another.
'handkerchief?' becomes 'hanky' ('hanky' can be a synonym of 'handkerchief').
'out' with letters rearranged gives 'tou'.
'tou' placed around 'hanky' is 'THANK-YOU'.
'there's' is the link.
(Other definitions for thank you that I've seen before include "show appreciation" , "Words of gratitude" , "Cheers" , "I'm grateful" , "Words of acknowledgement" .)