The first word of the headword phrase, the genitive plural kentili/wn, looks like a corruption of gentili/wn or genthli/wn, i.e. "gentiles". The phrase as a whole seems to be taken from the Passion of SS Sergius and Bacchus (web address 1), and appears also in its summary in the Synaxarion [summary of saints' lives] of the Church of Constantinople for October 7: "And St Sergius was the primicerius [highest ranking junior officer] of the School of the Gentiles, while St Bacchus was the secundicerius of the same school."
The "school" was in fact the regiment of horse-guards, originally consisting of non-Romans (Fowden 1999: 9). In Boswell's (1994: 375-390) well-known monograph it is rendered inaccurately as an educational institution.
[1] For this gloss see also mu 135, omicron 711, pi 2236, pi 2884, rho 77, sigma 153, sigma 452, sigma 1188, tau 785.