Language doctor up between two universities (4)
I believe the answer is:
urdu
'language' is the definition.
(Urdu is an example)
'doctor up between two universities' is the wordplay.
'two universities' means two substitutions for 'university'.
'doctor' becomes 'dr' (abbreviation).
'up' is a reversal indicator (in down clue: letters go upwards).
'between' means one lot of letters goes inside another.
'university' becomes 'U' (abbreviation as in UMass).
'university' becomes 'U' (abbreviation as in UMass).
'dr' written backwards gives 'rd'.
'u'+'u'='uu'
'rd' placed within 'uu' is 'URDU'.
(Other definitions for urdu that I've seen before include "Channel to north of Isle of Wight" , "Indian language" , "Language closely related to Hindi" , "Language akin to Hindi" , "Language spoken by Moslems in Pakistan and India" .)