Verb

sich entschließen

Translation

to decide, to resolve, to make up one's mind

Er entschloss sich, zu Hause zu bleiben.

He decided to stay at home.

Sie entschloss sich für das Studium.

She decided on the course of study.

Ich entschloss mich spontan zu der Reise.

I spontaneously decided on the trip.

sich ((zu+inf)) entschließen to decide ((to do sth.)) He decided to go.

sich ((für sth.)) entschließen to decide on ((sth.)) She decided on the red dress.

sich entscheiden (to decide), beschließen (to decide), bestimmen (to determine)

From 'ent-' (a prefix indicating beginning or finality) and 'schließen' (to close, to lock). The idea is to 'lock in' a decision.

Imagine 'closing' (schließen) all other options, leaving only the one you have resolved to take.