be on the house
if food or drinks are on the house, the owner of a bar or restaurant says you do not have to pay for them

[TahlilGaran] Dictionary of Contemporary English ▲

free something that is free does not cost you any money:
Parking is free after 6 pm.
‘How much is it to get into the concert?’ ‘Oh, I think it’s free.’
They were giving away free tickets for the concert.
I’m saving these tokens to get a free poster.
for nothing/for free without having to pay for something that you would normally have to pay for:
He offered to fix the car for nothing.
Fans were allowed into the stadium for nothing as a way of celebrating.
Children under five can see the show for free.
at no extra cost if a shop or company provides an additional service at no extra cost, they do it without asking you for any more money:
The shop will install the cooker for you at no extra cost.
Tours of the city are available from the hotel at no extra cost.
complimentary [only before noun] free – use this about things that a company, theatre, hotel etc gives people:
Karen’s sister works at the New York Ballet and she’s managed to get us some complimentary tickets.
Honeymooners receive a complimentary bottle of champagne in their hotel room.
be on the house if food or drinks are on the house, the owner of a bar or restaurant says you do not have to pay for them:
These drinks are on the house.
gratis especially written without having to pay for something:
Users will be able to listen to tracks (=songs)gratis.

[TahlilGaran] English Thesaurus ▲

on the house
if food or drink is on the house in a bar or restaurant, it is provided free by the owner.
We had to wait for a table so they gave us all gin and tonics on the house.

[TahlilGaran] English Idioms Dictionary ▲

on the house
paid for by the owner of a business; to be provided free by a business (usually a bar or restaurant)
We went to the restaurant and all of the drinks were on the house.

The hotel room was not ready when we arrived so they gave us drinks on the house.

[TahlilGaran] English Idioms Dictionary ▲

on the house
adj. phr., informal Paid for by the owner.
At the opening of the new hotel, the champagne was on the house.
Oscar was the first customer at the diner, so his lunch was on the house.

[TahlilGaran] English Idioms Dictionary ▲