What number when divided in half becomes zero?

I am looking for a word that change both gender and number when i add the letter 'S'.

What Word am I Looking For ?

The Brit lives in the red house.
2. The Swede keeps dogs as pets.
3. The Dane drinks tea.
4. The greenhouse is on the immediate left of the white house.
5. The greenhouse’s owner drinks coffee.
6. The owner who smokes Pall Mall rears birds.
7. The owner of the yellow house smokes Dunhill.
8. The owner living in the centre house drinks milk.
9. The Norwegian lives in the first house.
10. The owner who smokes Blends lives next to the one who keeps cats.
11. The owner who keeps the horse lives next to the one who smokes Dunhill.
12. The owner who smokes blue masters drinks beer.
13. The German smokes Prince.
14. The Norwegian lives next to the blue house.
15. The owner who smokes Blends lives next to the one who drinks water.
Now, the question is…Who owns the fish?

I have branches, but no fruit, trunk or leaves. What am I?

Which flower has two lips?

By moving exactly three matchsticks can you make the below equation true.It can be solved by 3 ways.

Three doctors said that Bill was their brother. Bill says he has no brothers. How many brothers does Bill actually have?

There are seven sisters in a house in a village where there is no electricity or any gadget.

Sister-1: Reading Novel
Sister-2: Cooking
Sister-3: Playing Chess
Sister-4: Playing Sudoku
Sister-5: Washing clothes
Sister-6: Gardening

what is Sister-7 doing ?

Place the numbers from 1 to 9 in the circles in a manner that each side of the triangle sums up to 17.

People put me on the table and cut me but do not eat me. What am I?