Toiling away at first developing engraved design (8)
I believe the answer is:
intaglio
'engraved design' is the definition.
(I've seen this before)
'toiling away at first developing' is the wordplay.
'away' becomes 'a' (abbreviation as used in sports fixtures).
'at first' means one lot of letters go next to another.
'developing' is an anagram indicator.
'toiling' after 'a' is 'atoiling'.
'atoiling' with letters rearranged gives 'INTAGLIO'.
(Other definitions for intaglio that I've seen before include "Printing process that uses an etched or engraved plate" , "Ligation (anag.)" , "artistic work" , "depressed figures?" , "Seal with a sunken design" .)