Polo enthusiasts sometimes do actually call them polOPonies.

Also it's a called a string because horses are sometimes tied out along a string-line. You run a rope between two trailers, and clip the horses' leads onto that "string". Like a picket line, only they don't strike. A rope hitching-rail.

Or sometimes they are exercised in a group on string leads, behind a lead horse whose rider holds the string. When you exercise a horse that way it's called "ponying."

I guess horse people would find music-jargon pretty strange as well.

~S~