Regardless of the absence of material (2,6)
I believe the answer is:
no matter
'regardless of' is the definition.
(I've seen this before)
'absence of material' is the wordplay.
'absence of' becomes 'no'.
'material' becomes 'matter' (synonyms).
'no'+'matter'='NO MATTER'
'the' is the link.
(Other definitions for no matter that I've seen before include "It's not important - what a torment" , "That is trivial" , "pure energy?" , "It's of little consequence - what a torment" , "Forget it!" .)