I. ˈmānˌlīn intransitive verb
Etymology: main line
slang : to inject a narcotic drug (as heroin) into a principal vein
• mainliner -īnə(r) noun -s slang
II. ¦ ̷ ̷ ˌ ̷ ̷ adjective
Etymology: main line , noun
1. : being part of an established group
mainline churches
2. : mainstream herein