Tls Crossword 1309 - Last Clue

[KathG]

I'm absolutely stuck on 6d, Verse form upsets one with a rhoticism (5). I have R-B-I. The only word that fits that is Rabbi, which is not a verse form, and while I tried searching I-B-R in the hope that upsets meant backward but no rational answer presented itself - I had been hoping there might be a name for people with difficulty pronouncing r sounds. I am fairly sure I have all the letters correct. Any help greatly appreciated as it is driving me mad.

[Mamyalynne]

Rubai (Verse form)

I a Bur, up

Bur, alt of Burr - to roll one's Rs (Rhotacism)

[Mamyalynne]

https://en.wikipedia.org/wiki/Ruba%CA%BFi

[KathG]

Thanks very much. I was somewhat thrown by my belief that rhotacism (odd, the spell check is insisting this should be rhoticism) was the word for the condition affecting people with problems pronouncing r sounds - indeed Jonathan Ross, who certainly pronounces r as if it were w, was given as an example in the online dictionary I use - whereas a burr, to me, is a tendency to sound the letter r very distinctly. I have one myself, as do most Scottish people. A correct perception might have led me to rubai via the Rubaiyat of Omar Khayyam.