an open-necked shirt

a red-necked grebe

swallow (something, especially a drink)

after necking some beers, we left the bar

by the end I was necking neat vodka and whisky

(of two people) kiss and caress amorously

we started necking on the sofa

form a narrowed part at a particular point when subjected to tension

the nylon filament necks down to a fraction of its original diameter