“Your honour,” said the plaintiff, “I’m no pontiff, but mister Cardiff, here held by the bailiff, is a real goniff.”
“Ah, go jump off a cliff,” shouted Cardiff, miffed. “Your honour, it was just a little tiff.”
“Tiff!” exclaimed the plaintiff. “You stiffed me! I bought a spliff from you, and when I complained it wasn’t the real stuff, you riffed on your supplier. But after I left, I came back and caught a whiff – you’d lit up in a jiff and were puffing away on a real reefer. When you had sloughed off chaff on me!”
“Oh, what’s the diff,” sniffed Cardiff. “We all got it tough.”
“Gentlemen,” interrupted the judge. “Given that selling and buying marijuana remains illegal in this jurisdiction, including soliciting such sales and purchases, the plaintiff must admit to a felony in order to make a complaint against the defendant. In short, mister Cardiff has commited a crime iff – if and only if – the plaintiff has. Does the plaintiff truly wish to pursue this action? …Do you get my drift?”
Ah, iff. By itself, a term from formal logic – meant for writing rather than saying – meaning “if and only if” (in other words, A iff B means that A and B inevitably go together – A is necessary and sufficient for B and vice-versa). But its form – a sound like a sniff, a huff, a good stiff cuff, or the sifting of chaff, and a shape like blowing wheat or puffing smokestacks – shows up at the ends of other words.
While it is not a proper morpheme, it does have a common origin in plaintiff and bailiff, tracing back to Latin ivus by way of French (it’s if in French): these are nouns indicating an action role. Pontiff also traces to Latin via French, but in this case it’s a shortening, from pontifex (French pontif). Nonetheless the word appears to be similarly a noun of role.
Goniff, which is one transliteration of the Yiddish for “swindler” or “thief”, may also be a noun of role, but its root is in Hebrew gannabh. Cardiff, which (aside from being a toponymic surname) is the English name of the capital of Wales, traces back to Welsh for “fort on the [river] Taff”.
But we do seem to like the double f rather than the single for the end of a word! It’s also standard for one-syllable words ending in a /f/ sound, whether they be clippings of longer words (diff, jiff; riff is from refrain), onomatopoeic or imitative formations (tiff, whiff, sniff, miff), good old Anglo-Saxon formations that just by arbitrary chance have the sound (stiff, cliff), or words the origin of which is uncertain (spiff, spliff). It’s simply an expected English pattern.
For all that, though, the word if has rarely been spelled as iff in English history, though it has had many spellings (gif or yif would be truer to its oldest form). And the logical operator iff “if and only if” has only been around for about a half a century. Aside from that, though it can produce impressions, it is not per se a morpheme – and it is certainly not the case that its presence has a necessary or sufficient relationship with some specific sense!