prettygoodword

terret (TER-it) - n., a metal ring on a horse's harness through which the driving reins pass.

So for context, if this isn't clear, these are the reins held by the driver of a wagon or carriage used to guide the leading horse(s). This could be on the collar or saddle of the leading horses or the bridles of horses not in the lead. I assume the same terminology is used if it's a wagon hauled by mules, but I haven't been able to confirm in the case of other animals such as oxen. You can clearly see one here, plus another less clearly:

Thanks, WikiMedia!

Alteration of earlier Middle English teret/toret, from Anglo-Norman turette, diminutive of Old French tur/tor/tour, circuit/ring/a round, related to turn.

(I have no memory of putting this on my list of words to run, so have no idea where I stumbled across it.)

---L.