Hot area crossed by girl in desert (6)
I believe the answer is:
sahara
'desert' is the definition.
(I know that Sahara is a desert)
'hot area crossed by girl' is the wordplay.
'hot' becomes 'h' (abbreviation eg on taps).
'area' becomes 'a' (maths abbreviation).
'crossed by' means one lot of letters goes inside another (inserted letters are crossed or covered by others).
'girl' becomes 'sara' (girl's name).
'h'+'a'='ha'
'ha' put inside 'sara' is 'SAHARA'.
'in' is the link.
(Other definitions for sahara that I've seen before include "Great African desert" , "World's largest sandy area" , "Hottest desert" , "About 3,500,000 square miles of Africa" , "Uncultivated region of north Africa" .)