Adding the suffix -less to the word flaw changes the word’s meaning to "without faults." "full of faults." "more faults." "the study of faults."

"without faults."

Explanation:

A suffix is a word particle that when added to the root of a word changes the meaning and sense of it. Learning the meaning of suffixes can be of great help when encountering unfamiliar vocabulary so that it can be easier to make an informed guess as to the meaning of the word.  

One of the most frequent suffixes is, indeed, “less”, and its meaning can broadly be condensed to: without.  

So, the word flawless comes to mean: without faults.