The Greek word ἑταῖρος
Word ἑταῖρος
he t a î r o ς
IPA hetaîroς
Meaning comrade, companion
See also Etruscan: etera ‘friend, partner, companion, client’
Synonyms ήλιξ

Other words that might be of interest
φρατήρ ‘brother, phratry member’