The dictionary (LINGVA, actually) says that "turn (a)round" means to turn through 180 degrees. How can one describe a turn through 360 degrees?

interesting question, indeed. Here is what I have found in Google:

A U-turn is a 180-degree turn.
"Turn around" usually refers to some kind of 180-degree turn.

"Turn around" can (but doesn't usually) also refer to a 360-degree turn, but people would usually add things such as "all the way" or "in a circle" etc. to make this clear.

When driving:
- He turned 180 degrees. = He made a U-turn.
- He turned 360 degrees. = He did a three-sixty. (Usually a form of reckless or out-of-control driving.) Shocked

If you are on your way somewhere and then turn back, you discontinue your travel to the originally planned destination and go back to where you've come from.

If you tell someone to turn around, that typically means the person should turn their back to you or vice versa (i.e. a 180-degree turn).

[www.english-test.net]

Hope this helps ~

How can one describe a turn through 360 degrees?

To make a full circle and come back to where the turn started?

[www.youtube.com]

Huge thanks to everybody and Merry Chistmas! But how shall I descibe a lamp that can turn around its axis? It must be a formal concise desription. Shall I write smth like "it can spin around its axis through 360 deg"? Will that be good enough?

turn/rotate through 360 degrees. "spin" suggests fast rotation!

Thank you, David. That is helpful.