n.
an imitation nipple used to soothe babies and toddlers; a soother, pacifier.
Type: 2. Preservation — Dummy is a shortening of the compound noun dummy teat (see OED-3, s.v. "dummy" (n.5f) and the 1904 quotation), where dummy means "imitation" or "fake". Dummy is a preservation in Canadian English from British English. In COD-2, the term is marked as both Canadian and British, while W-3 marks it as "chiefly British". Internet data show that although the term is also used in the US, it is most prevalent in Canada (see Chart 1). Soother and pacifier are the more common variants elsewhere (see Charts 2 & 3). Dummy can be considered a preservation in North American English.
See also COD-2, s.v. "dummy" (5), which is marked "Cdn & Brit.".