Jack up Definition 1 of 5Pro Tip 1/3Market Trends Used when discussing economics or market changes, indicating a strategic or forced increase. During the peak season, vendors often jack up the prices. Pro Tip 2/3Negative Connotation Often implies frustration or disapproval when prices are raised unfairly. Customers are upset because the store jacked up the price of milk again. Pro Tip 3/3Caution in Usage Avoid using in formal writing, as it can be seen as too casual or colloquial. I was surprised to see my bill had been jacked up without notice.