Select the Unabridged as your reference, and click on Advanced Search. Type fool into the Definition field and noun into the Function field and click on Search for 79 entries, ranging from ape to zany. Want to fool folks with some now-obsolete terms for fools? By going back to the Advanced Search screen and adding obsolete to the Usage Note field, the 79 terms with fool in their definition get winnowed down to 14 entries. Would you believe asinego? Tom tram?