Harmless gorilla's first seen in African country (6)
I believe the answer is:
benign
'harmless' is the definition.
(similar in meaning)
'gorilla's first seen in african country' is the wordplay.
'gorilla's first' becomes 'g' (1st letter of 'gorilla').
'seen in' indicates putting letters inside.
'african country' becomes 'benin' (country in Africa).
'g' going within 'benin' is 'BENIGN'.
(Other definitions for benign that I've seen before include "Kindly; not harmful" , "Obliging" , "Kindly, pleasant" , "Kindly or non-malignant" , "Favourable" .)