Putting my pedantic hat on (which I don't do very often but I know Ross is a stickler for accuracy in all things) I'd say Dummy is the standard word; or more often Dodo. I once cut the rubber teet off such a thing and submitted it to an exhibition of subversive art under the cunning title Dada Dodo - neet, eh? A teether is something very different (harder plastic ring for teething infant gumbs to chew on) and a soother can be both a teether and a dodo.