brido

The false seam first, because it is a good one. Esperanto has a real and productive suffix -id-, meaning the offspring of: ĉevalido is a foal, reĝido a prince, bovido a calf. Which makes brido look, to a learner three chapters into the affix track, like the child of a bro. It is not. A bridle is not a baby anything, bro is not a root, and the word is a single indivisible piece from French. The affix habit is exactly right and it will serve you well; this is one of the places it misfires.

In the literal sense it is the horse's headgear: the straps, the bit, the reins as a system. Bridi is the verb, to bridle a horse. Senbrida is unbridled, and it is a genuinely useful adjective.

The figurative sense came along with the metaphor and is fully standard in Esperanto, exactly as in English and French. You put a brido on your anger, your tongue, your spending. Bridi sin is to restrain oneself. It sits next to regi, to rule or control, but the flavour is different: regi is command exercised, bridi is force held back. A rider who is bridanta a horse is not driving it forward, and that is the whole point of the image.