rule of thumb saying meaning
rule of thumb. 1. a general or approximate principle, procedure, or rule based on experience or practice, as opposed to a specific, scientific calculation or estimate. 2. a rough, practical method of procedure. rule of thumb. 1. rule of thumb definition. A practical principle that comes from the wisdom of experience and is usually but not always valid: âWhen playing baseball, a good rule of thumb is to put your best hitter fourth in the batting order.â. Idioms and Phrases with rule of thumb.