“Poach” is a verb with three meanings.
The English poach (escalfar) eggs, and they sometimes have poached eggs for breakfast, “poached” being the adjective. One can also poach fish. A poacher (escalfador) is the type of pan that one may use to poach eggs.
One can go “poaching”, or “poach” (cazar en vedado), and the person that does such things is a “poacher” (cazador furtivo).
Sometimes there are “poachers turned gamekeepers (quardabosques)”. These are people who abandon something and do the opposite (que abandona una actividad para hacer lo contrario). For example, a thief becomes a policeman.
Finally, there is an idiom (modismo): “to poach on someone`s territory”, meaning you are stepping on somebody`s territory or area of responsibility (invadir o pisar el terreno a alguien).
So, you could have poached eggs for breakfast cooked in a poacher. You could then go poaching for a pheasant (faisán) for lunch, and the next day you decide to take a job as a gamekeeper – then you are a poacher turned gamekeeper.