Annotations to James Joyce's Ulysses/Hades/105

Annotations
De mortuis nil nisi prius.   (Latin) Of the dead [speak] nothing but before. Bloom is misquoting the Latin apothegm De mortuis nil nisi bonum (Of the dead [speak] nothing but good). He may be trying to adapt the saying to the idea he expresses in the same line, the implication being that one must wait at least two years before speaking ill of the dead.

He is probably also remembering vaguely the legal term nisi prius (unless previously), which refers to the court of original jurisdiction that heard a case as distinguished from a court of appeals.