The word “forgot” has several synonyms that can be useful in different contexts.
One synonym is “mislaid”. This often implies that you have misplaced or lost something and can’t remember where it is. For example, “I mislaid my keys and can’t find them anywhere.”
“Obliterated from memory” is a more dramatic synonym. It suggests that something has been completely erased from your memory. For instance, “The events of that day were so traumatic that they were obliterated from her memory.”
“Disremembered” is a somewhat old-fashioned or less common synonym. It simply means not remembering. “I disremembered his name until he reminded me.”
“Unremembered” is similar. It indicates that something has not been remembered. “The details of that trip are now unremembered.”
“Let slip from memory” is a more descriptive way of saying forgot. It implies that something has slipped away or escaped from your memory. “I let slip from memory the appointment I had made.”