An upper-class person, especially a Sloane Ranger.
"After years of working in factories, he finally managed to fit in at the exclusive golf club as a proper yah."
Yes.
"Yah, I'll be there by five o'clock."
An expression uttered to encourage a horse to run faster.
"The trainer shouted "yah!" as he urged his tired steed down the final stretch of the track."
Alternative form of Jah
"In his Rastafarian prayer, he referred to God as Yah instead of the more common spelling."