Briefly (2,5)
'briefly' is the definition.
(synonyms)
This is all the clue.
(Other definitions for in a nutshell that I've seen before include "essentially" , "To cut a long story short" , "Briefly, concisely" , "Brazil's location" , "to be concise" .)
(Other definitions for in short that I've seen before include "To sum up, briefly" , "Concisely" , "to be brief" .)
'briefly' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for in a word that I've seen before include "summing up" , "Where a number of characters may be found" , "Where letters are usually found" , "concise" , "Briefly - won raid (anag)" .)