These words, which are alike in being both nouns and verbs, are comparable in their denotation of the deliberate or involuntary distortion of a person’s facial expression because of displeasure, annoyance, pain or the like. Frown is the most familiar word. As visually perceived, a frown involves a knitting, contracting or wrinkling of the brows. As an expression, a frown can be a conscious or unconscious indication of displeasure or puzzlement.

• The teacher frowned with annoyance when a student fell asleep during his lesson.

Mostly, though, a facial frown is involuntary. It can be simple reaction to strong light: Many people who cannot wear sunglasses develop deep creases in their foreheads from frowning . A frown can also be the result of deep concentration or thought.

• The novel was very amusing, but it required so much attention that I often found myself frowning when I should have laughed.

In a figurative sense, frowning registers disapproval or distaste: to frown upon over-indulgence in food or drink.

The word with the most extensive application is grimace . A grimace is a distortion of the features, either habitual or momentary, that is caused by some feeling or impulse. It is usually ugly and uncontrollable, as when it is caused by pain or annoyance.

• The agonizing pain of arthritis gave his face a constant grimace ; A grimace appeared on the shopkeeper’s face every time a child approached the shelf of fragile articles.

But a grimace can be a deliberate attempt to provoke laughter, as when someone "makes a face": When the comedian’s lines fell flat, he resorted to grimacing to get laughter from his audience.

Although pout can refer to a general sullenness of behaviour, it more often is like frown in its designation of a special facial expression. Pout means to push out the lips, as in displeasure or ill humour. It is sometimes used in describing adults, but usually pout suggests the behaviour of a child.

• The little girl pouted all the afternoon because her mother had refused to buy her a new dress.

A scowl is a lowering of the brows, much like a frown . It can indicate the same kind of displeasure or annoyance that a frown does. But the emotions that generate a scowl are usually stronger than those that produce a frown . There is a strong suggestion of anger, a threatening quality, and certainly an air of sullenness in a scowl .

• His scowl hinted at the menace that lay behind his carefully modulated voice and calm demeanour.