Archi- \Ar"chi-\ [L., archi-, Gr. 'archi-, a prefix which is from the same root as 'a`rchein to be first, to begin; 'archh the first place, beginning; 'archo`s chief. Cf. AS. arce-, erce-, OHG. erzi-, G. erz-.]

A prefix signifying chief, arch; as, architect, archiepiscopal. In Biol. and Anat. it usually means primitive, original, ancestral; as, archipterygium, the primitive fin or wing.

Source: Webster's Revised Unabridged Dictionary (1913)