Administration > Environment Variables > APTACCEPTC — Specifying the Size of the Spelling Cache for Allowed or Learned Words
  
APTACCEPTC — Specifying the Size of the Spelling Cache for Allowed or Learned Words
Specifies the size (in words) of the spelling accept cache. For example, to set the word size to 300 words: set APTACCEPTC=300.
If this variable is not set, the Spell Checker assumes the cache size is 200 words. This means you can allow or learn 200 words (based on the assumption of 6 characters per word).