Horny beast and colonist run off together (8)
I believe the answer is:
antelope
'horny beast' is the definition.
'antelope' can be an answer for 'beast' (I've seen this before). I also know that 'horny' relates to this answer.
'colonist run off together' is the wordplay.
'colonist' becomes 'ant' (I've seen this before).
'run off together' becomes 'elope' (I've seen this before).
'ant'+'elope'='ANTELOPE'
'and' acts as a link.
(Other definitions for antelope that I've seen before include "Hoofed mammal" , "Graceful deer as a lone pet" , "Deer-like ruminant" , "Graceful ruminant - one leapt (anag)" , "Swift-running animal like deer" .)