GUAN-1

('guan' in the first tone)

关 = to close, closed, to turn off

The above single-character morpheme is indeed used as a word by itself.

A two-character version is:

关闭 = guan(1)bi(4)

Applied to a business or shop, 关闭 tends to mean that it shut down completely. When one wants to express that a shop closed for today, but will open again tomorrow morning, one should say:

关门 = guan(1) men(2) = to close, closed (lit. close the door) / these are two words

关于 = guan(1)yu(2) = about

于 = yu(2) = in, on, at (a standard preposition)

于 should not be confused with 干 = gan(1) = dry, or 干 = gan(4) = to do. The vertical stroke of 于 ends with a hook; the vertical stroke of 干 has no hook.