soother

Short definition from Wiktionary

Adjective

1. 1
   comparative form of sooth: more sooth, truer.

Noun

1. 1
   One who, or that which, soothes.
2. 2
   A pacifier; a plastic device that goes into a baby’s mouth, used to calm and quiet the baby.

Verb

1. 1
   To soothe.