After reading dozens of topics, I wanted to get a vote/informed opinions. It seems one of the most common whistle misconceptions is that “chiff” either IS breathiness, or is very closely related to breathiness.
From the topics I’ve read, chiff is more the “chirp” when changing notes than the quality of breathiness in tone.
Confirm/deny?
I thought chiff was pretty much the second thing you said. The crispness at the beginning of the note.
You know, I’ve stopped using “chiff” as a term of description, because it’s too ambiguous. And I’ve stopped assuming I know what someone else means when they use it. If you mean “breathiness” or “chirp”, say breathiness or chirp. 
In organ pipe terms, chiff is the non-harmonic transitional noise that occurs when air first enters the pipe and the note begins to sound. Since organ pipes don’t use finger holes (!), the chiff is a characteristic of the onset note whenever the pipe valve opens. It’s a breathy chirp.
Of course, you can produce the effect on a whistle by fingering a note and huffing into the whistle. But that’s not how whistle is played. There’s an element of breathiness to a sustained note, and there’s a chirp when the fingering changes from one note to another. Technically, neither one by itself is chiff.
If I had to pick one, I’d choose chirp as the closer analogue. After all, an organ pipe, like a whistle, may have a sustained breathiness apart from its onset chiff, and that’s a totally separate quality. But I think it’s best to avoid “chiff” altogether if you’re trying to communicate.
So I guess we should be Breathiness or Chirp and Fipple. And of course, “fipple” is not what people usually mean (the mouthpiece), but rather the block or plug (or equivalent) that forms the floor of the windway. So C&F = Breathiness or Chirp and Block or Plug. And now I’m going to go play my whistle …
My understanding is that chiff is indeed the ‘breathy chirp’ one hears on the attack on organ notes.
So chiff has something to do with breathiness, but not all breathiness is chiff. Speaking clincally, anyhow.
I think the term is sometimes used by whistlers to include the somewhat breathy sound
of some whistles. It’s a non-musical breathy quality to the instrument’s sound (not part of the note per se)
that some find pleasing. On this wider usage, chiff = breathiness. I guess I prefer the first
use, personally.
It never occurred to me until now, I’m embarrassed to say, that both “chiff” and "fipple’ are routinely misunderstood words. My recollection is that when I was looking for a title for the internet juggernaut which is C&F, I looked for the oddest and funniest sounding words I could find that had something to do with the whistle. They sounded pretty good together, in a funky sort of way. I almost called it “6-Hole Theory,” and, in fact, used that as the name of the last few issues of the newsletter.
…in case anyone is looking for a new avatar. 
I am deeply saddened to find the ambiguity unintentional. 
Here ya go~
“The Chiff that can be named is not the enternal Chiff.”
all these years I’m thinkin’ what a lovely sense of humor Dale has
an’ him just stringin’ funny words along. I’m crushed, I am!
I refuse to be part of an entity called “chirp and fipple.” I shall continue to use the term “chiff,” which we all should know is that wonderful little note attack semi squeaky sort of thingy ma jiggy whatsitswhositz.
Philo
Ahem… 
From an organ (the musical instrument) site comes the following:
“CHIFF: Part of the attack, or very first instant of speech, of a flue pipe. It is a clicking, consonant-like sound that serves to mark the entrance of each note in a moving passage. Chiff can be adjusted in voicing from being a very prominent part of the pipe’s speech to being completely inaudible. It is often called articulation, and when not excessive it increases the clarity of polyphonic music.”
Now what confuses me is “breathiness”. I’ve come to believe that it means one of two things:
That Clarke or Shaw sound, or
The sound I make when watching Andrea Corr playing whistle 
Fipple is just a funny sounding word that can only mean one thing. It’s that guy on C&F who makes the PVC flutes. Right?
aw no ya don’t… not Chirp & Tipple 
I move that we rename the juggernaut Snort and Suckle.
Has the virtue of utter clarity and seems to capture
succinctly what I do when I play a whistle.
Is there a second?
Here, here.
Where, where?
over hill,
over 
Chirp and breathiness is a good distinction.
For me personally, I would always want an instrument with as little inbuilt chirp as possible, because after all, that is what you get from a cut or strike - and I prefer to have it under control, not simply part of how the instrument sounds. Indeed, a lot of learning to play an instrument like the recorder (and so, for me, the whistle too) is learning to eliminate any extraneous sounds, especially in slurred phrases. Hence all the finger exercises - slurred scales and intervals. Then when your sound is pure, your cuts and so on really stand out a lot more. So I prefer a pure toned instrument without chirp or breathiness. (And, not to open up the old raging debate about cheap v. expensive, but this is one reason why I’m prepared to spend some money on a whistle, because the cheaper ones don’t seem to have that kind of tone).
But I know a lot of people prize the chirp and breathiness of certain instruments, which is fair enough.
Sorry, no can do.
My playing leads me to ‘Squeak and Dribble’.
Please, too much information