aterir

A defective verb, used almost only in the infinitive and as the participle aterido/a, meaning to become numb with cold — aterido de frío is the phrase you'll actually encounter, describing someone stiff and half-frozen. Conjugated forms outside the participle are vanishingly rare and feel archaic even to native speakers.

• Llegó a casa aterido de frío tras la tormenta. — He got home numb with cold after the storm.
• Los excursionistas quedaron ateridos en la cima. — The hikers were left frozen stiff at the summit.
• Se frotaba las manos, aterido, esperando el autobús. — He rubbed his numb hands, chilled to the bone, waiting for the bus.

Trying to conjugate aterir through a full regular paradigm — as a defective verb, it's really only used as aterido/a; for 'I'm freezing' right now, native speakers say tengo frío or me estoy congelando instead.