Meaning of RADAR in English

ra ‧ dar /ˈreɪdɑː $ -ɑːr/ BrE AmE noun

[ Date: 1900-2000 ; Origin: radio detection and ranging ]

1 . [uncountable and countable] a piece of equipment that uses radio waves to find the position of things and watch their movement ⇨ sonar :

The coastline can now be monitored by radar.

We could see the plane quite clearly on the radar screen.

2 . on somebody's/the radar (screen) if something is on your radar, you have noticed it and are giving it some attention:

This is one of the issues on our radar.

3 . fly/slip under somebody's/the radar to not be noticed by someone:

How did this band slip under the radar?

Longman Dictionary of Contemporary English.      Longman - Словарь современного английского языка.