This entry is wrong; it represents a misunderstanding or miscopying of the normal proverb as given by e.g. Hesychius kappa4861. The dice-throw Coös (the six of astragaloi or knucklebones; cf. alpha 4250) beats the throw Chios (the one-spot or ace), as Hesychius understands: *Kw=os *Xi=on: o( *Kw=os a)stra/galos, o( e(/c. o( me\n ga\r *Xi=os e)du/nato e(/n, o( de\ *Kw=os e(/c; "Coös (beats) Chios; the Coös (knucklebone) meant six, the Chian one." The Suda uncomprehendingly expands e(/c "six" into e)/cw "outside" and e(/n "one" into e)/ndon "inside", ignoring the rough breathings in the process (aspiration having been lost in Byzantine Greek pronunciation).
The gambling terms are also the adjectives from the place-names Chios and Cos, which gives rise to various jests. The adjective from Cos is written, however, usually, not always, with an iota subscript; the gambling term usually, not always, without -- for it refers to the hollow side of the knucklebone and is probably derived from the same root as the adjective koi=los "hollow". At Strabo 8.5.7 it means "cavern".
Taillardat discusses these throws (see Bibliography), especially the effect of throwing Chios after Coös, and suggests, contrary to Hesychius and this Suda entry, that Chios meant not a single ace but the throw of four aces and Coös the throw of four sixes. This would give a better sense to the proverb "Chios, standing beside, does not allow Coös" (reconstructed as *Xi=os parasta\s *Kw=on ou)k e)a=|), that, if you throw four aces directly after four sixes (trying, for example, for Euripides, the throw of 40), you lose the score of 24 for Coös.
Dionysus in Aristophanes, Frogs 968-70 describes Theramenes as the sort of lucky fellow who, when in extremis (e)s ta\ pa/nta), always falls (using the word in the gambling sense of a thrown dice) out of trouble and who uses the proverbial "Not a Chian, but a Cean". For the history and intertextuality of this proverb as applied to Theramenes see theta 345.