desconocer

To not know or be unaware of something (desconozco los detalles), or — its sharper sense — to fail to recognize someone or something you'd normally know: apenas lo reconocí, estaba irreconocible, casi lo desconozco. It can also mean to disown or refuse to acknowledge a person or claim (desconocer a un hijo, desconocer una deuda), a more formal, legal-sounding use.

• Desconozco los motivos de su decisión. — I don't know the reasons for their decision.
• Con esa barba, casi no lo desconocí... digo, no lo reconocí. — With that beard, I almost didn't recognize him.
• La empresa desconoció el contrato firmado hace años. — The company disavowed the contract signed years ago.

Despite the des- prefix, desconocer is not simply the opposite of conocer in a casual sense — it's more formal than saying no conozco/no sé, and its 'refuse to acknowledge' sense (desconocer una firma, desconocer a alguien) has no equivalent in a literal English translation of 'to un-know.'

Often confused with conocer.

• film Perfectos desconocidos — Álex de la Iglesia's 2017 Spanish remake of the Italian hit Perfetti sconosciuti — a dinner-party drama about secrets hidden in phones — became the highest-grossing Spanish film of that year and one of the top ten highest-grossing Spanish films ever by early 2018.