pentacosiarchus Save DMLBS pentacosiarchus [πεντακοσίαρχος = ‘commander of 512 men’] , by conf. w. pentecontarchus) leader or commander of fifty men. pentecontarche [ed. PL: pentecontarchi seu pentecosiarchi] Beleth RDO 12. 26c (v. pentecontarchus).