Meaning : A journey or route all the way around a particular place or area.

Example : They took an extended tour of Europe.
We took a quick circuit of the park.
A ten-day coach circuit of the island.

Synonyms : circuit

Meaning : A time period for working (after which you will be relieved by someone else).

Example : It's my go.
A spell of work.

Synonyms : go, spell, turn

Meaning : A period of time spent in military service.

Synonyms : duty tour, enlistment, hitch, term of enlistment, tour of duty

Meaning : Make a tour of a certain place.

Example : We toured the Provence this summer.