Final answer:
The synonym for 'tributary' as a noun is 'brook', which likewise denotes a small stream.
Step-by-step explanation:
The synonym for "tributary" as a noun is c) Brook. A tributary is a river or stream flowing into a larger river or lake, and the word brook similarly refers to a small stream.
The other options do not represent bodies of water: 'bent' typically means a predisposition or inclination, 'venture' is an undertaking involving risk, and 'drizzle' refers to light rain.