Crossword Genius

Untouchable item in bag, shade lower (6,3)

Ross

I believe the answer is:

sacred cow

I'm a little stuck... Click here to teach me more about this clue!

'untouchable' is the definition.
(I've seen this in another clue)

'item in bag shade lower' is the wordplay.
I cannot quite see how this works, but
'bag' could be 'sac' (a small bag) and 'sac' is present in the answer.
'shade' could be 'red' (red is a colour or shade) and 'red' is found within the answer.
'lower' could be 'cow' (something which lows - makes cow sounds) and 'cow' is located in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

(Other definitions for sacred cow that I've seen before include "One unreasonably held to be above criticism" , "Institution not to be criticised" , "Person, custom, etc unreasonably held to be beyond criticism" , "Much-guarded idea or institution, like Hindu bovine" , "one's above criticism?" .)

I've seen this clue in The Telegraph.
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