Ρ.
From LSJ
Γυνὴ τὸ σύνολόν ἐστι δαπανηρὸν φύσει → Natura fecit sumptuosas feminas → Es ist die Frau durchaus kostspielig von Natur
English (Autenrieth)
Many words beginning with ρ originally began with two consonants, esp. ϝρ or σρ (ϝρήγνῦμι, σρέω), and the quantitative (metrical) effect of the two letters has been preserved in the frequent doubling of ρ (ἔρρεον). What the initial consonant was cannot always be determined.
