Things you should know About Keywords: One word keywords are not very effective because they are not very targeted. In addition, the competition for these keywords is very high and it is very difficult to get good rankings for them. Web surfers might not use the keywords you expect. For example, people searching for "rhinoplasty" might actually enter "nose job" as the keyword. It is important to find the keywords that potential customers really use. Internet users who use four-word searches are more likely to purchase goods or services than those using fewer words (source: http://top10optimizer.com).
One word is called keyword More then one word is called Keyphrase Yes these days Keyphrase are actually being heavily searched
Exactly using a keyword may seem like a good idea but generally how many of you type in one word when surfing the web? I bet the number is vairly low. So a keyphrase would increase your chances of your site being noticed.
https://adwords.google.com/select/KeywordToolExternal I use that tool to find out what people type into Google. Type in ,for example, the word "money" and then you can look for phrases that are 4+ words. You can compete with those keyphrases.
Hmm, this was ong been discussed right?... If your aiming for a Keyword alone, think twice, you could get the results in a year because it's very hard to rank with it and it's very specific unlike in using a Keyphrase you could see the effects of your optimizing with-in a week or two...