I am saying is Wikipedia is well ranked for many terms in Google search results. In other words, this free content site is a source rich with relevant keywords for one single niche where you can do your long-tail keyword research.
How To Look For Long Tail Keyword From Wikipedia Articles
1. Firstly, I go to Google and type in the seed words together with the word wikipedia in the search box. (Example: acoustic guitars wikipedia)
2. From the search engine result page (SERP), you can find so many other related long-tail keywords. For instance: steel-string acoustic guitar, early romantic guitar, flamenco guitars, acoustic guitars are fitted with pickups, modern flattop, etc.
3. Some other words found in the SERP may not directly related to acoustic guitars, but these words are a good source for you to expand your keyword research. For instance: String Letter Publishing, transmit the strings' vibrational energy, etc.
4. Next, I click on the first search result on acoustic guitars.
5. Now look for keywords from the very first paragraph of the article. Just copy out whatever keywords you think you can explore further. For instance: diaphragm of the guitar, sound board, vibrations of the string, etc.
6. Now let's move to the article under “Contents”. You can click on the first item of the content, which is "Acoustic properties". From here, you can find more options for you to develop your keywords further. For instance: loudness of the guitar, plucking of the string, coupling and resonance effect, harmonic tones, different tonal qualities, etc.
7. And I also go the next item which is "Amplification" to grab for keyword ideas.
8. To drill down further, I click "References" under Content. For instance: Ovation guitar, guitar handbook, etc.
9. To find more keyword ideas, I click on "External links" and "Notes". And not forgetting the links to other related subjects.
Take your time you will be amazed with the amount relevant long-tail keywords you can find in Wikipedia.
* Here are more tools to look for keyword ideas.