Conceal source of flour in mixing guacamole (10)
I believe the answer is:
camouflage
'conceal' is the definition.
(thesaurus)
'source of flour in mixing guacamole' is the wordplay.
'source of' suggests taking the first letters (the start - or source - of the word).
'in' is an insertion indicator.
'mixing' is an anagram indicator.
The initial letter of 'flour' is 'f'.
'guacamole' with letters rearranged gives 'camoulage'.
'f' placed inside 'camoulage' is 'CAMOUFLAGE'.
(Other definitions for camouflage that I've seen before include "Disguise (from enemy)" , "Method of blending in fine" , "blind" , "Means of disguise" , "Disguise by use of colour, patterns etc" .)