Words about words

You twist something if you turn it around and around itself. Rope and yarn are made from thinner fibres twisted together. You twist jars to open them and you twist taps to turn them on and off.

Something or someone is ugly if they make you feel bad when you look at them.
The opposite of ugly is beautiful.

Uncommon means rare, strange or unusual. Uncommon is the opposite of common.

Albino squirrels like in the picture are quite uncommon.

Something is under something else if it is lower than it.
This cat is under the chair.
The opposite of under is over.

Something is underripe if it isn't ripe yet. Underripe fruit is usually green and hard.

You are undressed when you are wearing either no clothes or you are not wearing enough clothes. The people in the picture are undressed. When you are taking your clothes off, you are said to be getting undressed.
The opposite of undressed is dressed.

Someone is unfit if they are in poor physical condition, and get tired very easily when they do physical activity. The man in the photo is very unfit.
Unfit also means something that doesn't suit a purpose, for example a rotten fruit is unfit to eat.

Something is uniform if it is the same everywhere. A wall that is all one color might be described as being a uniform shade of green.
A uniform is also the name given to the clothing all people in an organisation have to wear so they all look similar. People in the military wear uniforms, and many schools require that children wear uniforms.
Uniforms for men and women are often quite different, even in the same organisation.

Someone is unkempt if they haven't paid attention to their personal hygiene and grooming, and look very scruffy. Something like a garden is unkempt if it has been unmaintained and left to get overgrown.

You unlock something when you open a lock, usually by using a key.