How can a man go eight days without sleep?

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

What Word am I Looking For ?

A worker is to perform work for you for seven straight days. In return for his work, you will pay him 1/7th of a bar of gold per day. The worker requires a daily payment of 1/7th of the bar of gold. What and where are the fewest number of cuts to the bar of gold that will allow you to pay him 1/7th each day?

Which is heavier: a ton of bricks or a ton of feathers?

If 1+9+8=1, what is 2+8+9?

This puzzle is for Harry Potter fans. Do you know why Tom Riddle is called Lord Voldemort?

If two fifty-foot ropes are suspended from a forty-foot ceiling that is twenty feet apart, how much rope will you be able to steal if you have a knife?

Can you find the odd one out from the below words ?

First Second Third Forth Fifth Sixth Seventh, Eighth Nine Ten Eleven Twelve.

Which organisation is a specialized agency of the UN that deals with global health issues?

a) World Trade Organization (WTO)
b) World Health Organization (WHO)
c) International Monetary Fund (IMF)
d) United Nations Educational, Scientific and Cultural Organization (UNESCO)

A couple went on a climbing trip. But only the husband returned from the vacation and said that his wife slipped off while climbing and died. On investigating, the local sheriff arrested him saying, 'Your travel agent called. You murdered your wife.'

The man did not inform anyone about the trip. Then how was the agent so sure that it was a murder?