How do I clear the terminal History?

I am using Linux Mint 17.1 Rebecca for about 2 days and accidentally typed my password into the terminal which is now displayed in the history list of commands I have previously typed.

I want to clear the terminal history completely. I have tried using the following commands in the terminal which I thought would clear the history forever but they do not:

history -c
reset
tput reset

The above commands "will" clear the history from the terminal but when I exit and bring up a new one all my previous history is still there and can all be listed again using the - history command and also by pressing the UP arrow on my keyboard. I do not want this to happen until I have totally cleared my history, then I want to continue using it.

How can I clear my terminal history completely - forever and start fresh?

Please Note: I do not want to exit the terminal without saving history just clear it forever in this one instance.