Pair crossing river that is in grassland (7)
I believe the answer is:
prairie
'grassland' is the definition.
(I know that Prairie is a type of grassland)
'pair crossing river that is' is the wordplay.
'crossing' means one lot of letters goes inside another.
'river' becomes 'r' (abbreviation for river).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'pair' enclosing 'r' is 'prair'.
'prair'+'ie'='PRAIRIE'
'in' is the link.
(Other definitions for prairie that I've seen before include "Schooners once crossed it" , "this oyster produces an egg" , "Extensive US grassland" , "Large grassland region" , "Tract of (US) grassland" .)