Annotations to James Joyce's Ulysses/Scylla and Charybdis/183

Annotations
absit nomen   (Latin) let the name be absent. Stephen is alluding to the Latin precept absit nomen, absit omen (If you do not utter an ill-omened expression, you will not incur the bad luck attendant on it). The second half of this phrase, absit omen (let there be no [ill] omen), is used on its own as an apotropaic phrase to ward off any possible bad luck that might attend the uttering of an ill-omened term; today one might knock on wood to achieve the same effect.