関 - CONNECT the Boards To BARRICADE the Relations!

Readings & Meanings:

カン

せき

concern, barrier

Common Usage:

下関（しものせき）

関係

関心

玄関先

Examples:

下関はふぐ料理で有名だ。

君には関係ないから、口を挟まないでくれ。

最近、クラッシック音楽に関心を持ち始めた。

玄関先に犬をつないでおいた。

Translations:

Shimonoseki is famous for fugu/pufferfish cuisine.

This doesn't concern you, so don't stick in your two cents (literally: stick your mouth in).

Lately, I've started having an interest in classical music.

I tied the dog to the entrance.

Radical:

門, the gate radical, is here.

That inner phonetic element used to be quite a bit more complicated: 關. That's 丱 and 幺, showing two boards connected by a thread/cord. That's where the "checkpoint, entrance barrier" meaning comes from. "Connect" is apparently a borrowed meaning.

References:

http://www.kanjinetworks.com/indices/radindex.html
http://www.thejapanesepage.com/node/kanji/7.htm