The offspring of two different species (6)
I believe the answer is:
hybrid
'the offspring of two different species' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for hybrid that I've seen before include "Crossbreed or mixture" , "Cross of two different species or varieties" , "Mongrel - cross" , "outcome of miscegenation?" , "Plant that is the offspring of two different species" .)