soñar

Soñar, with the ñ, means "to dream" - the dream you have asleep ("Anoche soñé con mi abuela" - Last night I dreamt about my grandmother) and the dream you chase awake ("Sueño con vivir en España" - I dream of living in Spain). Sonar, without the ñ, is a different verb altogether: "to sound, to ring, to go off" ("El teléfono no deja de sonar" - The telephone will not stop ringing).

The two are not related and are not even pronounced the same: soñar has the palatal ñ (as in "canyon"), sonar a plain n - so "I dream" is sueño, but "it sounds" is suena, never the other way round. They collide here only because the ASCII file slug for soñar has to drop its tilde, landing on the same string as the unrelated word sonar. Both happen to be -ar verbs with the same o>ue stem change, which makes the pair easy to muddle in writing even though no Spanish speaker would ever confuse them by ear.