puisne: Of a lower rank; an associate justice as distinguished from a chief justice. Before you hurt yourself trying to figure out how to pronounce it, here's a little help: it's French. From the old French puis (after) + né (born), it literally, or at least originally, designated someone born after someone else, hence younger. Puis is pronounced "pyoo."
Got the pronunciation yet? It's pronounced puny. In fact, puny and puisne come from exactly the same place etymologically. Of course, you can't refer to someone as puny in any official discourse without sounding unprofessional and egotistic, but referring to your underlings as puisne, well, that just makes you well-educated and intellectual.