Preposterous feature of the Discovery Channel (4)

I believe the answer is:

side

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

'preposterous feature' is the definition.
'side' can be an answer for 'feature' (side is a kind of feature). I am unsure of the 'preposterous' bit.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for side that I've seen before include "Dies (anag)" , "Ides (anag.)" , "Team; facet" , "Airs and graces" , "Team - border" .)

I've seen this clue in The Independent.

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