Gratitude for increase in value (12)
I believe the answer is:
appreciation
This clue could be a double definition.
'gratitude' is the first definition.
(I've seen this before)
'increase in value' is the second definition.
'appreciation' can be an answer for 'increase' (appreciation is a kind of increase). I am not sure about the 'in value' bit.
'for' is the link.
Can you help me to learn more?
(Other definitions for appreciation that I've seen before include "Rise" , "An expression of gratitude" , "Gratitude; increase in value" , "recognition" , "It is shown by applause" .)