Toggles the hidden bit on/off in the last created dictionary entry pointed to by dictionary address da.

: TEST ( -- ) 1 2 3 ;
' TEST >LINK HIDDEN
TEST

ERROR:
TEST not found

Note: At this point, it is not possible to re-instate the word by means of tick (') since the word is now hidden, and ' cannot therefore find it. To re-instate it, the address would have to be saved elsewhere.

When a word is hidden, dictionary searches with FIND will not find the word. Colon (:) hides new words during compilation so that new words may be defined in terms of identically named older words. Hiding the definition ensures FIND finds the old definition, not the new one. Semi-colon (;) un-hides the new definition (by executing HIDDEN again) at the end of compilation.