Jumble sale spreading sheer joy (8)
I believe the answer is:
pleasure
'joy' is the definition.
(I know that joy can be written as pleasure)
'jumble sale spreading sheer' is the wordplay.
'jumble' indicates an anagram.
'spreading' is an insertion indicator (inserted letters spread others open).
'sheer' becomes 'pure' (similar in meaning).
'sale' with letters rearranged gives 'leas'.
'leas' going inside 'pure' is 'PLEASURE'.
(Other definitions for pleasure that I've seen before include "A desirable emotion" , "A very desirable feeling" , "Urgent entreaty begins gratification" , "Delight, joy" , "Feeling of enjoyment or satisfaction" .)