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The word pas on its own is also used to negate phrases, for example: un hôtel pas trop cher a not-too-expensive hotel, a fairly cheap hotel
Nowadays, when a French person utters a phrase such as pas trop cher, the word pas is completely divorced from its meaning of "step", "pace". But once upon a time, the use of pas as a negative marker and its literal meaning of "step", "pace" were actually related.
Several centuries ago, the main way to mark a negative in French was via the word ne. As we've noted, in modern French, the word ne is essentially optional and carries little meaning. But originally, a sentence such as the following:
would have meant something much closer to "I'm not walking a single pace"-- i.e. it was the word ne that signalled that the sentence was negative, and pas essentially carried its literal meaning. Originally, other nouns than pas would have been used in this construction, and in fact various proverbs and archaic expressions still use ne ... mot ("not a word"), ne ... point ("not a stitch") and ne ... goutte ("not a drop"):
Qui ne dit mot consent
He who does not say a word consents (="silence gives consent")
Je ne pipai mot
I did not pipe up a word (="I kept mum", "I didn't say a word")
But, perhaps because certain nouns were more common in practice, over time, these nouns became re-interpreted as the actual negative markers, leaving ne as the somewhat redundant element that it is today.