neck·line 
/ˈnɛkˌlaɪn/ noun
plural neck·lines /ˈnɛkˌlaɪn/ noun [count] : the shape of the opening of a piece of woman's clothing around the neck
▪ The dress has a square/round neckline. ▪ a low/plunging neckline [=a neckline that leaves the top part of your chest uncovered]
▪ The dress has a square/round neckline. ▪ a low/plunging neckline [=a neckline that leaves the top part of your chest uncovered]
