From peri- + Poseidon. <span class="searchmatch">periposeidion</span> (plural periposeidia) Periapsis around Neptune. apoposeidion see periapsis...
From apo- + Poseidon + -ion. apoposeidion (plural apoposeidia) Apoapsis around Neptune. <span class="searchmatch">periposeidion</span> see apoapsis...