फ़्लैशकार्ड

The preposition on marks a calendar day or date as a surface in time. When you say on Monday, you indicate that an action occurs during that twenty-four-hour period. Adding an s to form on Mondays expresses a repeated habit or recurring appointment. In contrast, the preposition at pinpoints an exact moment on the clock or introduces a specific gathering. It never connects directly to a weekday name by itself.

Our supervisor scheduled the project review on Monday.