Guardian and Observer style guide: B
bete noire betting odds We frequently get this wrong. A brief explanation: long odds (eg 100-1 against, normally expressed as 100-1) mean something unlikely; shorter odds (eg 10-1) still mean it’s unlikely, but less unlikely; odds on (eg 2-1 on, sometimes expressed as 1-2) means it is likely, so if you were betting £2 you would win only £1 plus the stake. Take care using the phrase “odds on”: if Labour is quoted by bookmakers at 3-1 to win a byelection, and the odds are cut to 2-1, it is wrong to say “the odds on Labour to win were cut last night” – in fact, the odds against Lab...
Source: theguardian.com