Set at variance with effective distance (8)
I believe the answer is:
estrange
'set at variance' is the definition.
(thesaurus)
'effective distance' is the wordplay.
'effective' becomes 'est' (I can't justify this - if you can you should believe this answer much more).
'distance' becomes 'range' (I've seen this in another clue).
'est'+'range'='ESTRANGE'
'with' acts as a link.
Can you help me to learn more?
(Other definitions for estrange that I've seen before include "Get cut off" , "Antagonise using reagents" , "disunity" , "may break up" , "Lose friendship" .)