Big diversion, getting round desert (4)
I believe the answer is:
gobi
'desert' is the definition.
(I know that Gobi is a desert)
'big diversion getting round' is the wordplay.
'diversion' indicates an anagram.
'getting' means one lot of letters goes inside another.
'round' becomes 'o' (o is a circular letter).
'big' anagrammed gives 'gbi'.
'gbi' placed around 'o' is 'GOBI'.
(Other definitions for gobi that I've seen before include "Desert, mostly in Mongolia" , "Desert, cauliflower in Indian cuisine" , "The . . . . Desert is a barren plateau of S Mongolia and N China" , "very dry place" , "vast arid expanse" .)