I attempt to take in some equality of measure (8)
I believe the answer is:
isometry
'equality of measure' is the definition.
(I've seen this before)
'i attempt to take in some' is the wordplay.
'attempt' becomes 'try' (synonyms).
'to take in' is an insertion indicator.
'i'+'try'='itry'
'itry' enclosing 'some' is 'ISOMETRY'.
(Other definitions for isometry that I've seen before include "all being of equal stature" , "Equality of measure" , "equality of proportion" , "equal measure" , "having the same elevation" .)