Nipple (4)
I believe the answer is:
teat
'nipple' is the definition.
(I know that nipple can be written as teat)
This is all the clue.
(Other definitions for teat that I've seen before include "essential for babies" , "Nipple or dug" , "Bulb on infant's bottle" , "Part of feeding bottle" , "Piece on baby's bottle" .)