A person who is moonstruck or moonstricken has been affected by the moon. This effect on the mind can mean they are feeling romantic, lost in fantasy, or crazy and insane. This word originates from an ancient idea that the moon could cause madness. The word lunatic comes from the Latin word for moon (Luna), and even today, some people are suspicious of what can happen on a full moon. Example – The man at the bar had a moonstruck look on his face after drinking for several hours.

Source: ESL Vault