[macleginn]

A spelling error, using one dictionary definition, is "an error in the conventionally accepted form of spelling a word" --- mistaking one word for another does not fall under this definition. It is true that we now expect spell checkers to do grammatical checking as well, but a pure spell checker can indeed rely on a wordlist for English (this wouldn't work in languages with more developed morphology and/or frequent compounding).

[kmacdough]

Ok, but this is a technicality. Spell-checkers have slowly evolved into grammar checkers and what people really want is error correction. Whether people call it a spell checker a minor language issue (and the kind of things humans do all the time).

When teaching for your dictionary, ask: "is it obvious what they mean if I'm not being pedantic?"

[macleginn]

We expect different outputs in these two cases, though. A wrong word choice is usually accompanied by a hint that another word may have been intended, while a wrong spelling can be unambiguously marked as a mistake. These two behaviours can be turned on and off independently, and they need two different labels.

[ealexhudson]

Agreed. "Dessert" vs "desert" - mistaking these two is often not a grammatical error (they're both nouns), but is a spelling error (they have quite different meanings, and the person who wrote the word simply spelled it wrongly).

[macleginn]

I agree, but this is definitely the kind of spelling error (along with complementary/complimentary, discrete/discreet, etc.) that we normally don't expect our spellcheckers to catch.

[tacitusarc]

I don’t think I agree with your interpretation of the definition.

If I spell the word “pale” as “pal”, that is not an acceptable spelling for the word “pale”, even if it is coincidentally the acceptable spelling for an entirely different word.

If I asked a human editor to spellcheck the sentence: “His mouth dropped and he turned pal.”, the editor would correctly indicate I had misspelled the word.

Spellcheck hasn’t done this in the past because it can be quite difficult. But that’s a limitation of computer capability, not functionality bounded by the definition of the term “spellcheck”.