How is 潔{いさぎよ}い related to 清{きよ}い?
First, I'd like to point out this question: [潔]{いさぎよ}い meaning
Second, I've found a possible etymology for 潔{いさぎよ}い on gogen-allguide.
Gogen-allguide seems to say that いさぎよい probably comes from 甚{いた} + 清{きよし}, with いた expressing "to a great extent". Assuming I understood right, I don't quite see how this leads to the modern meaning(s) discussed in the other question.
I've also seen the word きよい written as 潔{きよ}い. This has me puzzled, too, because I'm not sure if it's supposed to express anything besides 清い. (My character dictionary doesn't list any such nuance, if so.) Is this a hint to the connection between these words, or a red herring?