litter

Where it comes from

Litter came through Old French litiere from Latin lectus, a bed. Medieval English used it for a bed and for a covered couch or bed carried on poles, the vehicle still called a litter.

How the meaning developed

A bed led to straw spread as animal bedding. Animals born together on that bedding became a litter, while scattered bedding supplied the route to odds and ends strewn about and eventually rubbish left on the ground. The medical carrying-litter revives the older bed-and-vehicle branch.

In use

A “litter” is a group of baby animals born together.
It does not mean the puppies are rubbish.
Before it meant puppies, the word meant a bed.

People called the straw animals slept on “litter”.
Then the name spread to the babies born together on that bedding.
From the bed to the babies lying in it.