治 - CONTROL the Rivers, HEAL the Dams

Readings & Meanings:

おさ（まる）

チ

ジ

to rule, govern

なお（す）

to cure

Common Usage:

治療

政治

治す

治安

Examples:

虫歯の治療をした。

政治のことに詳しい。

腕が外れたので治して欲しい。

NYの治安は昔に比べるとよくなった。

Translations:

I treated my cavities.

She knows a lot about politics.

I dislocated my shoulder, so I want that fixed.

The public peace in New York has improved a lot, compared to previously.

Radical:

Our old friend 水 is here in the San-sui on the left.

台 is normally, now, a counter for vehicles. Here, think of it as a pictograph showing heavy pressure (from above) on the ground.

Add 水 to pressure and you get "controlling the flow of rivers." This can feed into the meaning of "calm, settle down" as well as "to govern." Plus, if you are controlling a river that often overflows, you are "fixing" the problem, "healing" the cities damaged by flood.

References:

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