Partner once given plenty of warning (7)
I believe the answer is:
example
'warning' is the definition.
(as in making an example of someone)
'partner once given plenty' is the wordplay.
'partner once' becomes 'ex' (an ex-partner).
'given' says to put letters next to each other.
'plenty' becomes 'ample' (ample means enough or plenty).
'ex'+'ample'='EXAMPLE'
'of' is the link.
(Other definitions for example that I've seen before include "Someone to emulate" , "Something illustrating a general rule" , "Instance, specimen" , "Punishment" , "Specimen, sample" .)