Genitive singulars, the headword one presumably quoted from somewhere.
Latin magister appears in Greek in various forms: most often ma/gistros (alpha 2107 et al.), magi/ster (mu 16), magie/ster (mu 8), magi/stwr, and (as here) mai+/stwr. The loss of gamma before iota could reflect a sound change either in late Latin (cf. Italian maestro, French maître) or in Greek.