"Big weir" is a term that refers to a large structure built across a river to regulate its flow. However, there are many synonyms for this term that can add variety and interest to your writing. Some possible alternatives include "large dam," "massive barrage," "gigantic obstruction," "overwhelming barrier," or "titanic obstacle." Each of these phrases conveys a sense of impressive scale and power, which can help to add drama and tension to descriptions of rivers or waterways. Whether you are writing about natural landscapes or engineering marvels, using synonyms for "big weir" can help to make your words more vivid and memorable.