ap·si·dal \ˈapsədəl\adjective Etymology: Latin apsid-, apsis + English -al 1.: of or relating to the apsides of an orbit < apsidal motion > 2.[Medieval Latin apsid-, apsis + English -al]: of or relating to the apse of a church • ap·si·dal·ly\-dəlē also -dəlē\adverb