Belonging to a teaching organisation is ghastly, to be brief (2,1,8)
I believe the answer is:
in a nutshell
'ghastly to be brief' is the definition.
I can't tell whether this definition defines the answer.
'belonging to a teaching organisation' is the wordplay.
I cannot quite see how this works, but
'a' could be 'an' and 'an' is located in the answer.
'organisation' could be 'el' (el is a kind of organization) and 'el' is present in the answer.
'belonging to' could be 'in' (in can mean being a member of) and 'in' is located in the answer.
This explanation may well be incorrect...
'is' is the link.
Can you help me to learn more?
(Other definitions for in a nutshell that I've seen before include "where you'd find best part of Brazil" , "To cut a long story short" , "Brazil's location" , "Expressed briefly" , "essentially" .)