Penalized for a singular but not for a plural keyword form?

[mkassets]

I have a website ranking pretty high for all variations of widgets, all of them are low search volume and low competition keywords.

There is this strange thing I don't understand though. The site ranks #2 for "blue widgets" (without quotes) with the most relevant, blue widgets page, showing. However, when searching for the singular form "blue widget", the blue widgets page is nowhere to be found, and the homepage ranks near the position #150 !

Now, the singular form phrase certainly appears on the page few times, and I am quite sure overoptimization is not an issue either - nor on-page, neither in the incoming links anchors.

Are there any ideas what may cause this issue?

Thanks for your help.

[AnkitMaheshwari]

If the in-coming link anchors are equally distributed between blue widget and blue widgets then the internal linking might be influencing the difference of rankings along with the occurance/keyword density on the targeted page and competition for the two keywords.

[Mark_A]

I am looking at the same issues between blue widgets, blue widgetes and blue widget.

At the moment I am trying to optimise for all three of them which gets quite tricky on one page.

[tedster]

I often see pages where the singular and plural keywords are ranking quite differently. Especially for a competitive query term, that is not necessarily a penalty.

There are many possible reasons, but here's one that doesn't get talked about much. Google measures the user intention, and the intention for two versions of the same root word can often be different - informational search versus an intent to purchase, things like that. The algorithm treats different user intentions differently, and your page (or even your site) may not be the right "type" or taxonomy to match that intention.

So the query that the user typed in is also a ranking factor, and the ranking differences may not be about text matching the exact character strings.