denodarse

An archaic, literary reflexive verb meaning to strive boldly and persistently, to exert oneself with courage (se denodaba por salvar el negocio). It was common in medieval and Golden Age Spanish but today survives mainly in the adjective denodado ("bold," "strenuous," as in un denodado esfuerzo) rather than the verb itself.

• Se denodó por sacar adelante a su familia. — He strove doggedly to support his family.
• Los soldados se denodaban en la defensa de la ciudad. — The soldiers fought valiantly in defense of the city.
• Se denodaba en cada intento, sin rendirse. — He pushed himself hard in every attempt, without giving up.

Expecting to hear denodarse in modern conversation — it's genuinely archaic; even native speakers are far more likely to know the adjective denodado than to use this verb themselves.