a social gathering of people wearing masks and often fantastic costumes

disguise

Everyone is to go in masquerade — Horace Walpole

something that is merely show; pretence

In public they kept up a masquerade; though the marriage was increasingly loveless

to disguise oneself or to wear a disguise

(+ as) to assume the appearance of something that one is not

It's easy enough to put on a white coat and masquerade as a hospital doctor