Male creature crossing railway, an African antelope (4)
I believe the answer is:
oryx
'an african antelope' is the definition.
(I've seen this in another clue)
'male creature crossing railway' is the wordplay.
'male creature' becomes 'ox' (castrated bull).
'crossing' means one lot of letters goes inside another (to cross can mean to go over or around).
'railway' becomes 'ry' (abbreviation).
'ox' placed around 'ry' is 'ORYX'.
(Other definitions for oryx that I've seen before include "Animal" , "Large African antelope with long straight horns" , "creature" , "African long-horned grazer" , "horny beast" .)