Expressed gratitude twice in casual goodbye (4)
I believe the answer is:
tata
'casual goodbye' is the definition.
'tata' can be an answer for 'goodbye'. I'm not certain of the 'casual' bit.
'expressed gratitude twice' is the wordplay.
'expressed gratitude' becomes 'ta' (I've seen this in other clues. I am not sure about the 'expressed' bit.).
'twice' says to double the letters.
'ta' doubled is 'TATA'.
'in' is the link.
Can you help me to learn more?
(Other definitions for tata that I've seen before include "cheerio!" , "See you" , "So long!" .)