Onyomi words consisting of just one kanji (and nothing else)

Question

While using Rikaichan, one invariably notices all the words just consisting of one kanji character with its onyomi reading. However, most of these words seem to be barely used (at least in real conversations). It seems to me that most are only used in scientific papers as abbreviations for the respective jukugo of the same sense.

One character kanji words that are actually usable in conversation (and that don't make you sound super scientific) seem to be 敵, 詩、毒 and 罰, for example.　I think I've also heard 地, but there are other synonyms whose usage is definitely preferred. Furthermore there are some kanji that only seem to be used in fixed expressions like 気 in its various idioms and 念 in 念のために(so they don't really count here).

So, how should I think about these words? Are they just newspaper abbreviations (much like 独 for Germany, etc.) that shouldn't even be considered as real words? Are there any general guidelines which words one indeed can use in conversations (Or maybe even an explicit list of all such words which are common 話言葉、since there seem not to be too many)?

Answer 1

As I commented above, there are so many on-yomi words consisting of nothing else but single kanji. Let us start with those that even small children could use actively in their conversations.

・円{えん} = circle, yen

・駅{えき} = train station

・肉{にく} = meat

・服{ふく} = clothes

・本{ほん} = book

・変{へん} = strange

・列{れつ} = line (of people, objects, etc.)

・礼{れい} = bow, etiquette

・番{ばん} = turn (as in "It's my turn.")　

・席{せき} = seat

・曲{きょく} = song, tune

・県{けん} = prefecture

・行{ぎょう} = line(s) in writing

・会{かい} = gathering, event

Trust me, there should be many more.

Moving on to the ones it might take adult speakers to use actively..

・愛{あい} = love

・死{し} = death

・法{ほう} = law

・具{ぐ} = ingredient

・悪{あく} = evil

・軍{ぐん} = army

・恩{おん} = favor, moral indebtedness

・案{あん} = idea

Gotta stop here; It's past midnight.

Seriously, if I had the time and energy, I could make this list 10 times as long without much difficulty.

Answer 2

The fact that the overwhelming majority of on'yomi words is compound does not imply single-on'yomi-kanji words are rare.

Let's think about it in English. English has imported a huge number of Latin and Greek words, most of which is compound (though they aren't necessarily disassemblable in the scope of English). Picking up from your question: invariably (in-vari-abl-y), character (charac-ter), conversation (con-vers(-a)-tion) etc. Meanwhile, there are also many words that is likewise single words in original languages, and some among such shorter words are so basic and heavily used that hard to find replacement in present-day English, such as use, or sense, or sound, or fix, or just (all from your text too).

The situation is same in Japanese. Replace Latin with Chinese (on'yomi) and you'll get many basic words only take single kanji. The number is finite, but not sure if it's pointful to make a full catalog of them (though I don't know if you closely printed them on an A4 sheet with 6pt font...) Besides @l'électeur's great collection, I can easily think of any random word as much as you want:

客（きゃく） "guest; customer"
便（べん・びん） "a transport of car/train/plane/ship; convenience; feces"
図（ず） "figure; chart"
表（ひょう） "table; list"
文（ぶん） "sentence; passage"
塔（とう） "tower"
金（きん）・銀（ぎん）・銅（どう）・鉄（てつ） "gold, silver, copper, iron"
as well as 一, 二, 三, ... 十, 百, 千, 万, 億 etc. etc.

PS
気 and 念 you mentioned are not useless words alone. These words are merely being cast out from modern material life. If you read some fantasy or science fictions, you'll soon find 気 ("aura, energy, qi/chi") and 念 ("psychic, spiritual power") used all by their own.