What is the origin of this word?

He always wears a knit cap on cold days.

I'm feeling good today.

This bottle contains an unknown liquid.

His proposal was unilaterally refused.

I like to see old steam locomotives.

The war crime was condemned as inhumane by the international community.

It's difficult to understand his feelings.

We made a contribution to the local library.

The monkey was hopping from tree to tree, making an 'ook ook' sound.