Set up a route regularly crossing one continent or two (7)
I believe the answer is:
eurasia
'two' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'set up a route regularly crossing one continent' is the wordplay.
'set up' says the letters should be written backwards.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'crossing' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'continent' becomes 'sa' (abbreviation for South Africa).
The alternating letters of 'route' are 'rue'.
'a'+'rue'='arue'
'i'+'sa'='isa'
'arue' placed around 'isa' is 'aisarue'.
'aisarue' backwards is 'EURASIA'.
'or' acts as a link.
(Other definitions for eurasia that I've seen before include "combination of continents" , "large bloc of countries" , "Two continents considered as one" , "Unbroken landmass bearing two continents" , "Continental land mass" .)