"Quick on uptake" is a phrase that typically means someone who is able to understand things easily and quickly. Antonyms for this phrase would be terms that describe someone who is slow or struggles to comprehend information. Some antonyms might include "slow-witted," "dim-witted," "dense," "sluggish," "unintelligent," or "dull." These terms suggest a lack of mental agility or quickness and convey the opposite of the agile, sharp-minded people who can easily process information. It's important to remember that everyone has different skills, strengths and limitations. So, while some may excel at understanding new concepts quickly, others may require additional time or different strategies to comprehend the same information.