Extremely valuable tracks a great deal (4)
I believe the answer is:
very
'a great deal' is the definition.
Both the definition and answer are adverbs. Maybe they are linked in a way I don't understand?
'extremely valuable tracks' is the wordplay.
'extremely' means to remove the middle letters.
'tracks' becomes 'ry'.
'valuable' with its centre removed is 've'.
've'+'ry'='VERY'
Can you help me to learn more?
(Other definitions for very that I've seen before include "Extremely - light" , "Ever so" , "Frightfully" , "Truly" , "Real" .)