Purolator is an American company that manufactures oil and air filters. The name was taken from their oil filter process - "pure oil later".

In 1967, Purolator bought the Canadian courier company Trans Canada Couriers, which later took the Purolator name. The courier company was then later sold to Canada Post, but kept the Purolator name since it was commonly known in Canada.

Apparently, it's a holdover from being acquired by an oil filter company. Purolator = "pure oil later."

https://en.wikipedia.org/wiki/Purolator_Filters

The delivery company by that name was, at one point, owned by the Purolator oil filter company. (The shipping company used to be named Trans-Canada Couriers.)

Purolator comes from the phrase "pure oil later," as in long-lasting oil filters for combustion engines.