ι
From LSJ
Τὸ νικᾶν αὐτὸν αὑτὸν πασῶν νικῶν πρώτη τε καὶ ἀρίστη. Τὸ δὲ ἡττᾶσθαι αὐτὸν ὑφ' ἑαυτοῦ πάντων αἴσχιστόν τε ἅμα καὶ κάκιστον. → Τo conquer yourself is the first and best victory of all, while to be conquered by yourself is of all the most shameful as well as evil
Frisk Etymological English
ί
Grammatical information: pcle
Meaning: added particle, demonstrative-augmentative, ὁδ-ί, οὑτοσ-ί, νυν-ί etc. (Att.; also El. το-ΐ, Boeot. ταν-ί etc.), rarely -ίν.
Origin: IE [Indo-European] [285] *-i demonstr. pcle
Etymology: To be compared are the added enclitics Skt. and GAv. īm, ī; further -i in Hitt. aši, eni-, uni- the one mentioned, he, in Lat. utī etc.; Gothic has -ei. See Schwyzer 611 n. 3.