Venomous African country midge bites unknown number (9)
I believe the answer is:
malignant
'venomous' is the definition.
(thesaurus)
'african country midge bites unknown number' is the wordplay.
'african country' becomes 'mali' (Mali is an example).
'midge' becomes 'gnat' (I've seen this before).
'bites' means one lot of letters goes inside another.
'unknown number' becomes 'n'.
'gnat' going around 'n' is 'gnant'.
'mali'+'gnant'='MALIGNANT'
(Other definitions for malignant that I've seen before include "Bent on harming" , "Injurious" , "Feeling or showing great ill will, cancerous" , "Evil, malevolent" , "Spiteful" .)