Suntan I worked on, agony briefly (2,1,8)
I believe the answer is:
in a nutshell
'briefly' is the definition.
(I've seen this before)
'suntan i worked on agony' is the wordplay.
'worked' indicates anagramming the letters.
'on agony' becomes 'hell' (I can't justify this - if you can you should believe this answer much more).
'suntan'+'i'='suntani'
'suntani' is an anagram of 'inanuts'.
'inanuts'+'hell'='IN A NUTSHELL'
Can you help me to learn more?
(Other definitions for in a nutshell that I've seen before include "Summed up briefly" , "essentially" , "Neatly summarised" , "Briefly, concisely" , "Expressed briefly" .)