Related group that is equipped to see better? (7)
I believe the answer is:
species
'related group' is the definition.
'that is equipped to see better?' is the wordplay.
I cannot quite see how this works, but
'see' could be 'c' (the word for the letter, according to Chambers) and 'c' is found within the answer.
'that is' could be 'ie' ('i.e.' can be a synonym of 'that is') and 'ie' is present in the answer.
This explanation may well be incorrect...
(Other definitions for species that I've seen before include "Breed or genus" , "Sort, type" , "Kinds or sorts" , "Kind of creature" , "Groups of related plants or animals" .)