Animal eating bottom of anterior organ (6)

I believe the answer is:

breast

'organ' is the definition.
(breast is a kind of organ)

I don't understand how the rest of the clue works.

(Other definitions for breast that I've seen before include "flesh" , "Milk producer" , "Barest (anag.)" , "Milk-secreting organ" , "Cut of chicken" .)

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app