How is "burial" incorrectly formed?

Question

OED says that:

Middle English buryel, biriel, incorrectly formed as a singular of byriels, buriels n., q.v.; in later times associated with nouns in -al from French, such as espousal-s.

Etymonline.com says that:

"act of burying," late 13c.; earlier "tomb" (c. 1200), false singular from Old English byrgels "tomb," from byrgan "to bury" + suffix -els;

_{^{emphasis mine}}

How is the word burial incorrectly formed? What would be the correct form if it wasn't incorrectly formed?

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According to OED, buriels was used but it is obsolete now.

Here is the etymology of buriels from OED:

Old English byrgels strong masculine, cognate with Old Saxon burgisli neuter, < burg- ablaut-stem of bergan bergh n. to protect + suffix -isli- ; compare Old English græfels quarry, fætels purse, etc.

Answer 1

The answer is in the OED's definition of buriels¹, namely

1. A burying-place; a sepulchre, tomb.

2. An interment, funeral.

Note that both meanings are already singular: A burying-place, An interment, etc.

So the "correct" formation of burial would be buriels. It was "falsely" constructed because the singular, Old English word was mistakenly believed to be a plural, French word. From the OED's etymology of burial (just after the part you cited):

in later times associated with nouns in -al from French, such as espousal-s.

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¹ _{"ˈburiels, n." OED Online, Oxford University Press, June 2017, www.oed.com/view/Entry/24975. The etymology of buriels is helpful in pointing out how a singular English word ended up ending in -s (among other things). Note that the OED Online is unfortunately a prescription service (behind a paywall). However, many folks, especially in the UK, will have access through their local public library, and most students should be able to access through their institution's library. More info here: http://public.oed.com/about/free-oed/}

² _{"burial, n." OED Online, Oxford University Press, June 2017, www.oed.com/view/Entry/24969.}