'distributary' originates from Latin via English formations, ultimately based on Latin 'distribuere' (dis- 'apart' + tribuere 'to assign'), combined with the adjectival/nominal suffix '-ary' and influenced in form by the word 'tributary'.

'distributary' was formed in English by analogy with words like 'tributary' and from the verbal root related to 'distribute' (from Latin 'distribuere'); it became established in technical use (hydrology/geography) to name river branches that carry water away from the main channel.

Originally built from the idea of 'distributing' or 'dividing out', the term evolved to a specific geographical meaning: 'a branch of a river that distributes water away from the main channel'.