In reply to:

1 the strap of a horse‘s harness passing from the noseband to the girth between the forelegs, to keep the horse from rearing or throwing back its head: see HARNESS, illus.

Thanks for martingale, wwh. I haven't thought of that word in years. It's been such a long time since my daughter rode--and just seeing that word brought back the scent of the horses in the barn and all those girls dressed out for cross country. Very happy days, those were.