Pairs with 干流 (gànliú, main stem) or 主流 (zhǔliú, mainstream). Used both literally for rivers and figuratively for ideas, movements, or factions — a 'minor branch' or 'side current' away from the dominant trend.
memory
支 'branch' + 流 'flow/current' — exact same metaphor as English 'tributary' (Latin tribuere, 'pay/contribute' as a branch contributes water to a main river).
