If want to remove the word from only the start of the string, then you could do:
string[string.startswith(prefix) and len(prefix):]
Where string is your string variable and prefix is the prefix you want to remove from your string variable.
For example:
>>> papa = "papa is a good man. papa is the best."
>>> prefix = 'papa'
>>> papa[papa.startswith(prefix) and len(prefix):]
' is a good man. papa is the best.'