γυμνός gymnos means naked.
A Greek place where men study philosophy, read Homer and Hesiod, and train while naked.
Older conservative Jews completely rejected the gymnasium, but other Jews openly participated. As they had to be naked, their circumcision led to tension. Some covered their circumcision according to 1 Maccabbees, which was considered a rejection of the Covenant.
(Hillsdale College - Ancient Christianity)