An ambiguous word has more than one meaning, as such many words in English are ambiguous, but we generally refer to a word being ambiguous when it is ambiguous in a sentence, meaning the word could mean more than one thing even within the context of this particular sentence, rendering the sentence ambiguous, or open to multiple interpretations.
An ambiguation is an act of ambiguating something or a process by which something is made ambiguous.
An ambigu is similar to a buffet - in which several dishes are made available to someone, set on the same table, at the same time.
"Laissez les bon temps rouler." French ambiguation, btw.
The percent sign is an ambiguation of the number 100 meaning the number in question is a proportion of 100. Additionally 'per cent' means 'of one hundred'. Its origins lie in ancient Greek, though there is no clear indication of a single person introducing the sign.