From metecho; participant, i.e. (as noun) a sharer; by implication, an associate -- fellow, partaker, partner.
see GREEK metecho
1. sharing in, partaking of, with the genitive of the thing (Winer's Grammar, § 30, 8 a.): Hebrews 3:1; Hebrews 6:4; Hebrews 12:8; τοῦ Χριστοῦ, of his mind, and of the salvation procured by him, Hebrews 3:14; cf. Bleek at the passage
2. a partner (in a work, office, dignity): Hebrews 1:9 (from Psalm 44:8