”気” in Japanese, pronounced “ki”, represents something like “natural energy”, though it can also mean “air” or “atmosphere” in some cases. A similar word is used in many other Asian cultures, including Chinese (‘Chi’ or ‘Qi’), Korean, Vietnamese, and Thai. The large character pictured above is a more complex version of more the commonly used 気 character, and has the same meaning.
By no means will I attempt an explanation of this heavy philosophical/spiritual concept, which interlinks tightly with some forms or medicine and martial arts (for example 合気道, which roughly translates to “the way of fitting together energy”). For those that want to learn more, see the Wikipedia page on Qi to get a basic introduction to “ki”. But regardless of whether you understand it, or even believe in it, “ki” is a concept used very frequently in the Japanese language, and to attain any level of fluency you will have to learn many expressions which utilize it.
I don’t know the exact numbers, but I believe there are over 100 expressions containing the word 気、and would guess there are several hundreds, if not thousands, of kanji compounds which contain it.
Having said that, there are a handful of expressions which are used frequently enough that it will be of great advantage to you to memorize and master. Knowing these will also increase your ability to express yourself (what is known in Japanese as 表現力).
気にする：Literally “Make into energy”. Used to when you worry about, be concerned with, or care about something.
- 過去なんて気にするな
- Don’t worry about the past
気がする: Used when you have a feeling about something.
- 僕が勝つ気がする
- I feel like I’m going to win
気になる: “Becomes energy”. Used when something worries you or catches your interest/curiosity.
- そのアニメが気になる。
- I’m curious about that Anime series.
気をつかう: “Uses energy”. Hard to translate, but this one expresses a feeling of ’emotional burden’ or ‘weight’, or something that makes you emotionally tired. It means you have to expend mental energy when you are around them.
- 友達と一緒に住むのは気を使うね。
- Living with friends takes an emotional toll.
- 結婚相手は気を使わなくていい人が理想。
- For a marriage partner, a person who you don’t have to act around (can be yourself) is ideal.
気がちる: “Energy scatters”. Used when you can’t concentrate because something is distracting you.
- 周りがうるさいと気がちって勉強できない
- When it’s noisy around me, I get distracted and can’t study.
気に入る: ”Put into energy”. Used to mean something that is liked or a favorite. Noun form: お気に入り
- このアイスが気に入ったよ
- I like this ice cream.
気がつく：”Energy sticks”. Used when someone realizes something. Noun form: 気づき
- もう夜の１０時だって気づいた
- I realized that it is already 10 PM.
気が合う: “Energy fits”. Used to mean getting along with someone, or being on the same wavelength.
- 彼女と気が合いそうだからつき合ってみたら？
- Since it seems like you get along well with her why don’t you ask her out?
気がある: ”Have energy”. Used to mean someone has an interest in another person, romantically or sexually.
- 君に気があるって聞いたよ
- I heard (she/he) is interested in you.
References
http://en.wikipedia.org/wiki/Qi
http://dictionary.goo.ne.jp/leaf/je2/15273/m0u/%E6%B0%97/
The Image use in this post was taken from this page, licensed as Wikimedia Commons: http://en.wikipedia.org/wiki/File:Ki_obsolete.svg
