Etymology of ひざまずく

Question

I can't resist trying to find patterns in words. These three words, for example, seem to fit a similar pattern:

• 頷{うなづ}く　= [項]{うな} + 突{つ}く (source: community wiki)
• 躓{つまづ}く　= [爪]{つま} + 突{つ}く (source: community wiki)
• 額{ぬか}づく　= [額]{ぬか} + 突{つ}く (source: gogen-allguide)

However, I can't seem to find the etymology of 跪{ひざまづ}く anywhere. Since it appears to fit the pattern, I'd like to guess:

• 跪{ひざまづ}く = [膝]{ひざ} + ま + 突{つ}く

But where does the ま come from? It doesn't seem to fit the pattern neatly like the others.

Answer 1

It would be nice to have some more authoritative sources on this topic (if there are any), but I'm not convinced there is. A lot of the pages I could find said they don't know where it comes from, and I'm not sure anybody really does...

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But one theory may be, in the Wikipedia article for 膝{ひざ}, it says:

...つま先と膝をついて座る座り方は「跪く」と言い...

A rough translation of that might be:

"...the way of sitting that is falling on your knees and toes and sitting down is called '跪く'..."

So I think it may be a combination of 膝{ひざ}, 爪{つま} and 突{つ}く.

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I'm a bit sceptical of the "best answer" at this link (other pages say "つ" in "つまづく" comes from "爪" rather than "蹴" for example), but this seems to be more-or-less what one of the non-accepted answers at this Chiebukuro question says, saying that "〜まずく" is "つまづく" and that "つまづく" comes from "爪{つま}" and "つく".

Answer 2

I first thought of ま being 真 and, indeed 跪く is written as 膝真づく on this page of a sapphire sculpture of a kneeling person. That's the most likely guess.

You might enjoy the answers to this question. It would be great if you were to add this one and your other findings to that page in a separate answer.