counter for laps or circuits
Used to count laps around a track, circuits of a course, or rounds of a competition.
I run one lap around the track.
I did three laps around the park.
このコースを三周走った。
I ran three laps of this course.
Mathematical term for the length of the boundary of a shape.
Find the perimeter of this rectangle.
Zhou dynasty; Chou dynasty
Historical term referring to the Zhou dynasty of ancient China (approx. 1046–256 BCE).
The Zhou dynasty lasted for about eight hundred years.
I went all the way around the island by bicycle.
周 is the everyday counter for laps around a track or course, while 巡 is a more literary word for rounds or cycles, as in patrol rounds.
周囲 is the ordinary noun for 'surroundings' or 'circumference', while 周 as a math term refers to the perimeter length itself.
回 is the general counter for occurrences or times, whereas 周 specifically counts completed laps or circuits of a course.
周 (a lap/circuit) and 週 (a week) share the same reading しゅう but have completely unrelated meanings, so learners must rely on kanji and context to tell them apart.
Standard kanji form for all senses.
The kanji 周 originally depicts a border or enclosure, giving rise to meanings related to circumference, perimeter, and cycle. The counter use for laps derives from the idea of going around a circuit.