Tighten up Definition 1 of 3Pro Tip 1/3Physical Adjustments Used when describing adjustments to the tightness of material things. After losing weight, he had to tighten up his belt. Pro Tip 2/3Literal Tightening Refers to physically making something more snug, often with hands or tools. The maintenance crew needed to tighten up the bolts to prevent leaks. Pro Tip 3/3Easily Overlooked Sometimes used for small but important adjustments that could easily be forgotten. I need to tighten up the laces on my sneakers before the race.