While both "late" and "tardy" describe arriving after the expected time, there's a subtle difference. "Late" is a general term and can be used in many situations. "Tardy," however, usually implies being late for something scheduled, like a class or a meeting, and often carries a slightly more negative connotation, suggesting a lack of punctuality or even a slight disregard for the schedule.
Here are some example sentences to illustrate the difference:
Late:
Tardy:
Notice that while both words can describe an arrival after a scheduled time, "tardy" often has a stronger implication of blame or a need to improve one's time management skills.
Happy learning!