Own special son coming in is nuisance (4)
I believe the answer is:
pest
'is nuisance' is the definition.
(I've seen this before)
'own special son coming in' is the wordplay.
'own special' becomes 'pet' (I am not sure about this - if you are sure you should believe this answer much more).
'son' becomes 's' (genealogical abbreviation for son).
'coming in' indicates putting letters inside.
'pet' enclosing 's' is 'PEST'.
Can you help me to learn more?
(Other definitions for pest that I've seen before include "Destructive creature" , "Disease with a high death rate" , "Destructive insect or nuisance" , "Annoyance" , "Menace" .)