While 开关 (kāiguān) is a modern, technical term, its structure offers a window into Chinese linguistic philosophy. Unlike the English word “switch,” which has its own opaque etymology, 开关 is transparent. You can see its meaning just by looking at its parts. This reflects a common pattern in Chinese of creating complex words from simple, concrete concepts. The pairing of 开 (kāi) and 关 (guān) is a fundamental duality, much like Yin and Yang (阴阳). They represent opposite states: on/off, start/stop, active/inactive. Recognizing this pattern of combining opposites (like 大小 dàxiǎo - size, from big/small) or related concepts will help you unlock the meaning of hundreds of other Chinese words. In a Western context, we might think of an “on/off switch” as a single object. The Chinese term forces you to think of it as a device that embodies two distinct, opposite actions: the potential to open a circuit and the potential to close it.
开关 is an extremely common and practical word you'll encounter daily.
The single most common mistake for learners is using 开关 (kāiguān) as the verb for “to turn on” or “to turn off.” 开关 is the noun (the switch itself). 开 is the verb (to turn on). 关 is the verb (to turn off).
Think of it this way: You use the 开关 (kāiguān) to 开 (kāi) the light. The noun is the tool; the single character is the action.