Complex sentence: It probably means "sixth" (cf. Latin "sextus", "sixth") Parallels are the Roman names Secundus, Tertius, Quintus, Septimus, Decimus, etc. Note that these names do not necessarily denote the order in which their bearers were born.
Split into simpler sentences: It probably means "sixth" (cf. Latin "sextus", "sixth"). These names do not necessarily denote the order in which their bearers were born.