Character for washing the face

It means washing the face in Classical Chinese. The word is a learned, old-fashioned way to name this ordinary act.

The related form 沬 appears in oracle-bone writing—inscriptions carved on bone or turtle shell—as a person washing at a basin. Bronze inscriptions on vessels show hands, a basin, water, and a face. The Shuowen dictionary, an old Chinese character dictionary, treats 頮 as an ancient written form of 沬 and explains it as hands scooping water to wash the face.

The Book of Documents, an early Chinese classic, uses 頮 in a scene where a king washes before ceremonial clothes are put on.

What does 頮 mean when someone sends it?

Read it as a classical word for washing the face. If someone sends 頮 alone, you can decode the word but not why they chose this old-fashioned vocabulary.

Older Classical Chinese assigned different verbs to washing the hands, face, hair, body, and feet. Later, broader washing verbs took over some of those uses; 頮 remained a precise literary choice.