n.
an imitation nipple used to soothe babies and toddlers; a dummy, a pacifier.
Though COD-2 (s.v. "soother") marks the term as both Canadian and British, internet search results indicate that dummy and pacifier are the more prevalent variants in Canada (see Charts 1, 2 & 3). As Chart 1 shows, soother appears to be, together with Britain, the least prevalent in Canada, while dummy is very frequent in the .ca domain (Chart 2), as is the originally American term pacifier.
See also COD-2, s.v. "Soother"(1), which is marked "Cdn & Brit".
See also: dummy
- 1913  Where did they gather the fivers from, pet?
Where will they gather the millions more yet?
Fivers don't grow on the green wattle bough--
Where will they gather those fivers, and how?
Tax on your nightie, and tax on your shawl,
Tax on your binder, and booties, and all--
Tax on your bottle and soother and groats,
Tax on your gown and your ribbon and coats.
Tax on your cradle, and tax on your cot,
Tax, heavy tax, on the sweet sugar-pot--
Tax on the cottage from ceiling to floor,
Tax on the roofing and tax on the door. 
- 1939  Lastly, Mr. Bracken would be well advised to have his German equipment in Canada before he parts with his butter and honey or he may find himself landed with half a million babies' soothers because "German metallurgical industry must exclusively be devoted to combatting Britain's wicked encirclement policy," or some such excuse. 
- 1978  Eating from the Tree of Knowledge in this garden is no more dangerous than taking a drag off a baby soother, and all sexual tensions have been eliminated by soaking in the warm bathwater of optimistic ideology. 
- 1987  Dr. Stephane Schwartz has just pulled 12 rotten teeth from the mouth of a 20-month-old baby, a child still in diapers and just learning to say "mama, papa."
Later, at a Christmas party for staff at the dental clinic of the Montreal Children's Hospital, the dentist says the mother confided she kept a soother coated in honey in the child's mouth. 
- 1999  Gretzky display has everything but 'a soother, a soiled diaper': Hockey Hall of Fame unveils its largest exhibit ever for one individual and includes several mementoes from No. 99's past.; [Final Edition] 
- 2009  Soothers have been offered to babies for hundreds, if not thousands of years. Mothers have long been aware that sucking provides comfort to babies. Sucking rags were an early incarnation of today's soother and were made by wrapping a piece of cloth around a piece of meat, fat, or a stale piece of bread. Yum!
Soothers have long been thought to interfere with breastfeeding so many families opted not to offer them to their infants. Several years ago research indicated that soothers can decrease the risk of SIDS by as much as 61% so more parents are making the choice to offer a soother to their baby. The difficulty often comes when the SIDS risk period is past but your baby has developed an attachment to the soother.