Slime, for example, covering wildebeest's back (5)
I believe the answer is:
gunge
'slime' is the definition.
(both can mean a sticky substance)
'example covering wildebeest's back' is the wordplay.
'example' becomes 'eg'.
'covering' is an insertion indicator.
'wildebeest' becomes 'gnu' (synonyms).
'back' says the letters should be written backwards.
'eg' enclosing 'gnu' is 'egnug'.
'egnug' in reverse letter order is 'GUNGE'.
'for' is the link.
(Other definitions for gunge that I've seen before include "Sticky stuff (colloq.)" , "Goo" , "Wet sloppy stuff" , "Thick sticky muck" , "Messy, slimy substance" .)