The young actor delivered his lines trippingly, as if he had practiced them a thousand times.

trippingly 是由动词 trip 加后缀 -ingly 构成的副词形式。trip 本意是"轻快地行走"，引申为"流畅地、轻快地"。 trippingly 在这里形容台词说得"流畅自然、轻快自如"，带有一种轻松不费力的感觉。