Though the names of different parts of animal anatomy, the terms may have, in part, a common explanation.
That is, the dewclaw is that rudimentary inner claw, sometimes present in dogs, which hangs loosely in the skin above the other toes and which brushes, not the soil, but only against the “dew” on the grass.
Similarly, the dewlap of cattle, dogs, or turkeys is the lap or fold of skin hanging loosely under the throat, and which, some say, brushes against the “dew” on the grass.
In this latter term, however, others think that the element dew is a corruption of some word that can no longer be traced.