David Bloom writes to point out that Wiktionary has adopted eggcorn as a technical term, at least in the etymology for helpmate:
The OED's etymology for helpmate is a bit more circumspect:
< help n. or help v. + mate adj.; probably influenced in origin by helpmeet n.
David observes that
… "helpmate" seems to be a double eggcorn, the original "helpmeet" having a pretty comical etymology in its own right.
The Wiktionary's version of that etymology:
From a misinterpreting of the phrase in Genesis 2:18 "an help meet" for Adam (i.e. suitable for him).
And the OED's etymology, which agrees while providing a bit more historical detail, along with some editorial evaluation:
A compound absurdly formed by taking the two words help meet in Gen. ii. 18, 20 (‘an help meet for him’, i.e. a help (help n. 2) suitable for him) as one word.
Already in the 17th cent. the Scripture phrase is found with the two words improperly hyphened; which led the way to the use of help-meet , helpmeet , without ‘for him’. But its recognition as a ‘word’ is chiefly of the 19th cent.: it is unknown to Johnson, Todd, Richardson, and to Webster 1832. In the 17th cent. they used more grammatically meet help , meet-help : compare sweet heart , sweetheart .
The origin of "helpmeet" as a re-analysis of a phrasal fragment is certainly eggcorn-like, but something else is going on as well. I can't offhand think of any other "compound[s] absurdly formed" in a similar way, but there must be some.