American english: bus paint can TV antenna mail (maybe also "snail mail"...implies physical mail) graduate school/ postgraduate school--either, but graduate school is more specific and points towards a school where you'd receive a terminal degree thermos (flask has connotations of a container for alcohol in the US) package student

I would say both components of all the sets can be used interchangeably.In India we study British English but are also exposed to the American form and so it doesn't matter which one is used as long as the message goes through.

bus transport/ bus transportation (transportation) paint tin/ paint can (tin/can varies by region) TV aerial/ TV antenna (antenna or aerial antenna depending on circumstance) mail / post (as a noun and verb) -- We mail a letter using the US Postal Sevice, the Brits post a letter using Royal Mail. graduate school/ postgraduate school -- both depending on circcumstance. thermos/ flask -- both ; a thermos is insulated, a flask usually isn't, & as said above, usually refers to alcohol parcel/ package -- depends on circcumstance . Officially services are often refered to as parcel services, but we'd say "There is a package on the porch for you." pupil/student ---- both depending on circ. skipping rope/ jumping rope (the sport itself) -- both kindergarten/ nursery school -- both BUT nursery school is before kindergarden and is not required by law; kindergarden is the year before 1st grade and is required by law.