Nothing around - sort out an opening (7)
I believe the answer is:
nostril
'an opening' is the definition.
(I know that nostril is a type of opening)
'nothing around sort out' is the wordplay.
'nothing' becomes 'nil' (eg nil is zero in football).
'around' means one lot of letters goes inside another.
'out' indicates an anagram (out can mean wrong or inaccurate).
'sort' with letters rearranged gives 'ostr'.
'nil' placed around 'ostr' is 'NOSTRIL'.
(Other definitions for nostril that I've seen before include "Nasal opening" , "Nose hole" , "Part of nose" , "Nasal aperture" , "Nasal passage" .)