a piece of jewelry that is pinned onto the wearer's garment
"She fastened her red silk flower to the lapel of his suit jacket with a silver pin."
a number you choose and use to gain access to various accounts
"I forgot my banking pin, so I can't log in to check my balance until tomorrow when I reset it at the ATM."
cylindrical tumblers consisting of two parts that are held in place by springs; when they are aligned with a key the bolt can be thrown
"The locksmith spent an hour picking the pins to bypass the lock without needing the original key."
a small slender (often pointed) piece of wood or metal used to support or fasten or attach things
"She carefully placed a wooden pin through the fabric layers to hold them steady before sewing."
a club-shaped wooden object used in bowling; set up in triangular groups of ten as the target
"He adjusted his stance to aim for the center pin at the head of the rack."
A needle without an eye (usually) made of drawn-out steel wire with one end sharpened and the other flattened or rounded into a head, used for fastening.
"The chemist decided to pin the new compound during the meeting so everyone would know it was using the standard nomenclature system."
Acronym of personal identification number.
Initialism of preferred IUPAC name.
In plain English: A pin is a small, sharp piece of metal with a flat head used to hold things together or fasten clothing.
"She clipped her notes to the front of her shirt with a silver pin."
Usage: As a noun, pin refers to a small object with a sharp point and a flat head used to fasten fabric or hold things together. The chemical initialism PIN stands for Preferred IUPAC Name and should not be confused with this common household item.
to hold fast or prevent from moving
"The child was pinned under the fallen tree"
(chess) immobilize a piece
"The player sacrificed his queen to pin the bishop and prevent it from defending the king."
To fasten or attach (something) with a pin.
"The old blacksmith was seen pinning down the hot iron to shape it before hammering it into a sword blade."
Alternative form of peen
In plain English: To pin something is to hold it firmly in place using a small sharp object.
"She pinned the photograph to the bulletin board with a thumbtack."
Usage: Do not use "pin" as a verb to mean striking or shaping metal with a hammer; that action is correctly spelled "peen." Instead, reserve "pin" for actions involving fastening something in place with a pin or keeping it fixed.
The word "pin" comes from Old English, where it originally meant a peg or bolt. It traveled into modern English with this same core meaning of a small, pointed fastener.