Feat: continue to improve documentation

docs/forth/definitions.md

@@ -58,6 +58,19 @@ You can even redefine numbers:
 
 Now `2` pushes `4` onto the stack. The number two no longer exists in your session. This is a classic Forth demonstration: nothing is sacred, everything can be redefined. 
 
+## Removing Words
+
+`forget` removes a user-defined word from the dictionary:
+
+```forth
+: double dup + ;
+3 double           ;; 6
+"double" forget
+3 double           ;; error: unknown word
+```
+
+This only affects words you defined with `:` ... `;`. Built-in words cannot be forgotten.
+
 ## Practical Uses
 
 **Synth definitions** save you from repeating sound design: