Chemist Boots' opening during festival (5)
I believe the answer is:
nobel
'chemist' is the definition.
(I've seen this before)
'boots' opening during festival' is the wordplay.
'opening' suggests taking the first letters.
'during' indicates putting letters inside.
'festival' becomes 'noel' (I have seen 'Religious festival' mean 'noel' so perhaps 'festival' could also mean 'noel').
The initial letter of 'boots' is 'b'.
'b' inserted within 'noel' is 'NOBEL'.
(Other definitions for nobel that I've seen before include "& 27 Down International award" , "Alfred -, Swedish dynamite inventor" , "he provided prizes" , "-- Peace Prize" , "Swedish prize" .)