To follow behind something or someone, or to drag or pull something behind; to move slowly or fade away.
From Old French 'traîller' or 'trahir,' possibly related to 'trail' meaning to drag. Used in English since medieval times with the sense of following a path or dragging something.
When your voice trails off, it's literally doing what it sounds like—following behind and disappearing, just like someone trailing behind a group, making it one of those verbs that sounds like the action!
Complete word intelligence in one call. Free tier — 50 lookups/day.