The term 'opposite of on' can be expressed in two ways: 'AGO' and 'OFF'. 'AGO' is a three-letter word meaning 'before the present time or before a specified time in the past'. It is often used to refer to a period of time that has passed, such as 'five years AGO'. 'OFF' is also a three-letter word meaning 'not on; away from a place or position'. It is often used to describe something that is not in use or not functioning, such as 'the lights are OFF'. Together, these two words provide an accurate description of the term 'opposite of on'.