lojala

One root, and the law inside it is real but not Esperanto's. Lojala looks for a moment as though it might have something to do with leĝo, and the instinct is right about the history and wrong about the language. Latin lex, legis gave legalis, legalis became Old French loial, and loial became loyal. So the connection is genuine etymology - but it happened entirely in French, centuries before Esperanto existed, and by the time Zamenhof borrowed the word it was a single unanalysable root. Loj- is not leĝ- plus anything, and there is no seam to break it on. This is the same class as inspiri: true cousins in Latin, strangers in Esperanto.

The fence with fidela is the one that matters.Fidela is faithful - it is about attachment, and it stretches to a dog, a spouse, a friend, a translation. Lojala is about honouring an undertaking: a law, a contract, an oath, a set of rules you agreed to play by. A dog is fidela, not lojala. A business competitor who does not cheat is lojala, not fidela. Where English loyal covers both feelings at once, Esperanto makes you choose, and the choice is usually obvious once you ask whether there is an agreement in the picture.

The second sense follows from the first. Because it starts with rules, lojala slides easily into fair, straight, above board: lojala konkurenco is fair competition and is a fixed phrase in Esperanto commercial writing, exactly as concurrence loyale is in French. Lojaleco is the abstract noun, mallojala its opposite - disloyal, and also unfair in that commercial sense - and perfidi is the verb for what a mallojala person eventually does.