"Lookers-on" is a term used to describe people who observe an event or situation without participating in it. However, there are various synonyms that can be used to refer to these individuals. One common alternative is "spectators," which implies a passive role of watching and witnessing. Another synonym is "onlookers," which has a similar meaning to "lookers-on." "Observers" is also a suitable synonym that conveys a sense of detachment and neutrality. "Bystanders" is another word that can be used to refer to individuals who are present but not directly involved in an event or situation. Ultimately, the choice of synonym will depend on the specific context in which it is being used.