Agree with you on purity, but not modesty. The term has been completely co-opted to be all about how revealing a womanβs clothing is (and frequently beyond that to how sexually attractive a woman is in her clothing).
Biblically, it is about not showing off in your clothing to draw attention to wealth, and that sense is also much more accessible from the usual meaning of the word, which is to do with being humble in general.
I think modesty encompasses both still, because I think it's about not showing off, whether it is showing wealth through the expense or relative social status through one's appearance. Also, if i remember correctly, some of Paul's encouragement towards modesty is addressing cities where temple prostitutes were very wealthy and showed it by their clothes and braiding gold chains into their hair. The implication could be "don't dress like a prostitute," which can lead to a more modern-evangelical purity culture definition.
Either way, by showing off the expense of clothes or by revealing oneself seems to be jockeying for status, which seems to go against the spirit of modesty.
