To sum up, I go under about hiding answer (2,1,4)
I believe the answer is:
in a word
'to sum up' is the definition.
(I've seen this before)
'i go under about hiding answer' is the wordplay.
'go under' becomes 'drown' (I've seen this before**).
'about' says the letters should be written backwards.
'hiding' means one lot of letters goes inside another.
'answer' becomes 'a' (abbreviation eg in Q and A).
'drown' written backwards gives 'nword'.
'nword' going around 'a' is 'naword'.
'i'+'naword'='IN A WORD'
(Other definitions for in a word that I've seen before include "Where a number of characters may be found" , "summing up" , "Where letters are usually found" , "To summarize" , "To summarise very briefly" .)