Plaintive describes a sound that expresses sadness or longing, like it's carrying a quiet plea or complaint. When a dog makes plaintive whines at the door, you can hear the sadness in its voice as it asks to come inside. A plaintive melody in a song might make you feel a little melancholy, as if the music itself is sighing.

The word comes from an old word meaning “to complain,” but plaintive isn't about angry complaining. It's softer than that: more like the sound of missing something or wishing things were different. A violin can play plaintive notes that seem to ache with emotion. A bird might make plaintive calls when separated from its flock.

You might hear plaintive tones in someone's voice when they're asking for something they really hope for but aren't sure they'll get. The word captures that particular quality of sadness mixed with longing, like the feeling in your chest when you hear a train whistle in the distance on a quiet evening.