μῦ
From LSJ
ἀγεωμέτρητος μηδεὶς εἰσίτω → no one ignorant of geometry may enter, let no one ignorant of geometry enter, let no one ignorant of geometry come in
English (LSJ)
τό, name of the letter μ, IG2.4321.24 (iv B. C.), Epigr. ap. Ath. 10.454f, Hellad. ap. Phot.Bibl.p.530 B., etc. 2 μῦ or μὺ μῦ, to represent a muttering sound made with the lips, μῦ λαλεῖν to mutter, Hippon.80 (dub. l.); to imitate the sound of sobbing, μὺ μῦ, μὺ μῦ Ar.Eq.10.