The phrase "study at sly" can be used to describe someone who is being sneaky or secretive in their studying habits. Some synonyms for this phrase include "study in secret", "study clandestinely", "study covertly", "study furtively", and "study surreptitiously". These words can be helpful when trying to describe someone who is trying to hide their learning from others or who is studying in a way that might not be socially acceptable. Whether you are trying to describe someone who is studying for a test or for personal growth, these synonyms can help you convey the meaning of the phrase "study at sly" in an effective way.