1. A textual error produced by a mental error.
2. A mental error.
The word was formed by analogy and due to a shared vowel sound from typo (typographical error).
I used this word for over a decade before I finally decided to post a definition and clarifying discussion on a message board (which is now gone due to a site change).
This is my earliest description I could find, from a post on 31 Oct 2000 to a Regency email list:
Another class of error, which I call a mindo through parallelism with a typo, is a mental error. Spoonerisms and Malapropisms are both kinds of mindos. Mindos that affect manuscripts include spelling errors, grammar errors, historical errors, and any other error of fact or usage that the author believes to be correct. The nature of this whole class of errors makes them likely to be missed no matter how many times an author reads a manuscript.
For sense 1, the severity of the error depends on the effect on the text. Word substitution errors are among the most common mindos that reach publication. Many word substitutions, spelling errors and grammatical errors have minor impact because skimmers may not even notice them and gestalt-readers mentally correct them while reading because the intended word, spelling or usage is fairly obvious. Some word substitutions where the intended word isn't obvious and some grammatical errors create problems when the substituted word or grammatical error changes the meaning.
When a substituted word is only a letter or letter-pair different from the intended word, one can't say for certain whether the error was a typo or a mindo.
Observed examples that could be typos or mindos:
Abjure / Adjure
Access / Assess
Acetic / Ascetic
Adit / Audit
Adjoin / Adjourn
Adverse / Averse
Affect / Effect
Allowed / Aloud
Allude / Elude
Altar / Alter
Loath / Loathe
Palatable / Palpable
Shudders / Shutters
Tinkling / Twinkling
Vaulted / Vaunted
Yoke / Yokel
Observed examples that I think are clearly mindos:
Admirably / Admiringly
After / Before
Again / Ago
Algorithm / Logarithm
Allusions / Delusions
Alpha / Beta
Ancestors / Descendants
Anecdote / Antidote
Antagonist / Protagonist
Aspersion / Dispersion
Cache / Cash
Collaborate / Corroborate
Dentition / Detention
Ministrations / Ruminations
Paramount / Tantamount
Peanuts / Peasants
Questionably / Questioningly
Sextant / Sexton
Unexpected / Unsuspecting
Sense 1 errors are produced by sense 2 errors.
For sense 2, there are variations in both duration and severity.
Acute or transient or momentary mindos are brief. The thinker / speaker / writer knows the correct word or proper grammatical usage but fails to use it in a particular instance.
Intermittent mindos come and go. The thinker / speaker / writer learned something poorly or unclearly and sometimes gets it right and sometimes gets it wrong. I suspect that lay/lie errors (far and away the most common errors I saw in a decade of tracking errors seen in published books) are intermittent mindos for many English-speakers. (I have seen books with lay and lie used correctly and incorrectly in both directions. It is faintly possible that errors in one direction came from a writer and errors in the other direction came from a copy-editor, but more likely that the writer simply couldn't remember proper usage.)
Chronic mindos are false beliefs: things we know that aren't so. The thinker / speaker / writer simply got a fact or usage wrong. Chronic mindos produce text errors that the writers can NEVER correct because they don't think they are errors--these are errors that must be caught by editors and beta readers.
Bad guesses and ignorance might be classified as chronic mindos. In text, these show up when a writer has no specific knowledge about something yet writes whatever they assume or think they know. Examples include details of plant and animal life cycles, native locations or dates of introduction of plants and animals, modern language in historical fiction set before the words were coined, local geography, etc.
Trivial mindos don't matter a lot. Most (but not all) sense 1 mindos have trivial real-world impact.
Serious mindos can have real-world impact on people's lives.
Dangerous mindos can actually endanger people's lives.
Fear of vaccines is an example of a dangerous mindo. There has been an increased failure since the 1990s to use available vaccines due to widespread misinformation and failure to understand modern science. A major source of misinformation was a since-discredited scientific paper years ago that questioned the safety of a vaccine (it turned out that the author of the paper had a competing product). Failing to get a flu shot contributes to many deaths from severe influenza every year. Parents preventing their children from getting many standard vaccinations endangers those children and endangers everyone through the reduction of "herd immunity" (the protection of all people from epidemics and pandemics by having a high enough percentage of the population immune due to vaccination).
Global warming denial is another example of a dangerous mindo. I went into great detail on this years ago.
In politics: is a lie a mindo? When politicians take totally inconsistent positions on an issue at different times, have they honestly forgotten what they've said or are they cynically expecting voters to forget? The GOP has treated limited government and privatization as nearly sacred ideas, despite much evidence of the falsity of their claimed virtues. Is clinging to political and economic ideas that endanger the country a mindo or should stronger words be used?