fromEnglish Grammar Today
Holidayas a singular nouncommonlyrefers to a specific day or event:
It’s a publicholidayon Monday, isn’t it, so I suppose the banks’ll be closed?
She seems very tired and upset at the moment. She needs aholiday.
We booked aholidayonline yesterday – two weeks in Greece.
We use the plural nounholidaysandholidayin similar ways:
We are all going to Croatia for ourholidaysthis year.
We are all going to Croatia for ourholidaythis year.
We often useonwithholiday:
They’re very good friends. We first met them when we wereon holidayin Morocco.
Not: …when we were in holiday… or …when we were at holiday… or …when we were on holidays…