What is the name of the instrument with a set of plucked tines played using the thumbs?

The instrument being referred to is the kalimba, which is also known as a thumb piano. It consists of a wooden board or resonator box with metal tines of varying lengths that produce different pitches when plucked with the thumbs. This unique playing technique not only allows for melodic performance but also involves a percussive element since the tines vibrate to create sound.

In contrast, the piano requires the use of keys that are struck with the fingers, while the cello is a string instrument played with a bow and is held between the knees. The accordion is a free-reed instrument that is played by compressing and expanding a bellows, producing sound through keys or buttons. Each of these instruments has its distinct mechanics and methods of play, making the kalimba the only one that specifically matches the description of being plucked with the thumbs.