On reflection, lives to regret crossing area, a huge one (7)
I believe the answer is:
eurasia
'huge one' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'on reflection lives to regret crossing area a' is the wordplay.
'on reflection' is a reversal indicator.
'lives' becomes 'is' ('be' can be a synonym of 'live').
'to regret' becomes 'rue' (to rue something is to regret it).
'crossing' means one lot of letters goes inside another (to cross can mean to go over or around).
'area' becomes 'a' (maths abbreviation).
'is'+'rue'='isrue'
'isrue' enclosing 'a' is 'isarue'.
'isarue' backwards is 'eurasi'.
'eurasi'+'a'='EURASIA'
Can you help me to learn more?
(Other definitions for eurasia that I've seen before include "Germany and Japan are in it" , "Large northern hemisphere land mass" , "Combined continent" , "large bloc of countries" , "Unbroken landmass bearing two continents" .)