One who or that which pacifies. [1913 Webster]
A small device, usually of rubber or plastic containing a protruding nipple-shaped portion which a baby may place in its mouth and suck on; -- it is used to keep babies contented. [PJC]

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OXFORD DICTIONARY

pacifier, n.
1 a person or thing that pacifies.
2 US a baby's dummy.

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THESAURUS

pacifier

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