To kiss and caress amorously. They spent the evening necking on the couch.
To form a narrow part in a container or object. The bottle was necked to create a more ergonomic design.
Slang. To drink (something), especially directly from the bottle, quickly or in one continuous motion. She necked the soda before heading back on stage.
To kill (a bird) by quickly breaking its neck. The farmer necked the chicken before preparing it for supper.