When we talk about a large quantity of something, we often use the phrase "be numerous". However, there are a variety of synonyms that can be used to convey the same or similar meanings. Some possible alternatives for "be numerous" include: abound, proliferate, teem, swarm, overflow, brim, and fill. Each of these words implies a sense of plentifulness or abundance in different ways. For example, "teem" suggests a sense of vitality and activity, while "overflow" implies that something is spilling over its usual boundaries. By using synonyms for "be numerous", we can add variety and nuance to our writing and speech.