Sometimes you'll see somebody brag about how many words are in their spell-checking dictionary. It turns out that having too many words in a spell checker's dictionary is worse than having too few.
Suppose you had a spell checker whose dictionary contained every word in the Oxford English Dictionary. Then you hand it this sentence:
Therf werre eyght bokes.
That sentence would pass with flying colors, because all of the words in the above sentence are valid English words, though most people would be hard-pressed to provide definitions.
The English language has so many words that if you included them all, then common typographical errors would often match (by coincidence) a valid English word and therefore not be detected by the spell checker. Which would go against the whole point of a spell checker: To catch spelling errors.
So be glad that your spell checker doesn't have the largest dictionary possible. If it did, it would end up doing a worse job.
After I wrote this article, I found a nice discussion of the subject of spell check dictionary size on the Wintertree Software web site.
[Raymond is currently on vacation; this message was pre-recorded.]