Purely oral nutrient, strangely including whiskey (9)
I believe the answer is:
unwritten
'purely oral' is the definition.
(spoken as opposed to written)
'nutrient strangely including whiskey' is the wordplay.
'strangely' is an anagram indicator.
'including' means one lot of letters goes inside another.
'whiskey' becomes 'W' (phonetic alphabet: alpha, bravo, charlie etc.).
'nutrient' is an anagram of 'unritten'.
'unritten' going around 'w' is 'UNWRITTEN'.
(Other definitions for unwritten that I've seen before include "Not put down on paper" , "Based on custom rather than documentation" , "without script" .)