ETIMOLOGY

Safety Pin:

The word Pin, comes form the late old english word, pinn "peg, bolt,"
before 1100, Middle English pinne, Old English pinn  peg; cognate with Dutch pin, German Pinne, Old Norse pinni and  perhaps from Latin pinna  (feather, quill).
In dictionary:

Pin;

1.
a small, slender, often pointed piece of wood or metal,  used to fasten, support, or attach things.
2.
a short, slender piece of wire with a point at one end and a head at the other, for fastening things together.
3.
any of various forms of fasteners or ornaments consisting essentially or partly of a pointed or penetrating wire or shaft (often used in combination): a jeweled pin.
4.
a badge having a pointed bar or pin attached, by which it is fastened to the clothing.


Safety pin;

1.
a pin bent back on itself to form a spring, with a guard to cover the point.

Safety;

1.

the state of being safe; freedom from the occurrence or risk of injury, danger, or loss.

2.

the quality of averting or not causing injury, danger, or loss.

3.

a contrivance or device to prevent injury or avert danger.

Safety was an adjective, added to the word Pin, in order to identify one of its characteristics, provide security to (something).