I don't believe that Hugh Tracey coined the term thumb piano although he may have used it when trying to promote lamellaphones amongst Europeans who would have been more familiar with the term. I am pretty sure it came from the missionaries whose only reference was the piano which they used to teach 'natives' to sing christian hymns.

Thumb piano is a most unsuitable term for an instrument which has nothing in common with an instrument where keys are struck which cause hammers to strike strings. The term mbira (which Hugh Tracey as far as I can remember argued should be the generic term) also has some problems since it refers only to Zimbabwean instruments and more specifically to the mbira dzavadzimu. There is additinal confusion in that mbira in Zimbabwe refers both to the specific instrument, the mbira (dzavadzimu) or mbira huru and to the generic type. Even the Tonga refer to their instrument as mbira although the proper name is kankobela or kanamala. The widespread use of the term mbira has much to do with the ubiquity of the mbira dzavadzimu and the cultural dominance of the Shona in Zimbabwe.

The term lamellaphone (offically but incorrectly spelled lamellophone) is a good generic term that was devised by Prof Gerhard Kubik (in the 70s?) because it is not culture-specific and describes the 'tongues' of the instrument.

The problem is further compounded by the fact that the terms mbira, mbila, marimba, malimba karimba, kalimba, timbila, valimba etc. all come from the same basic root and can refer to xylophones or the mbira in different situations. The classifaction system works on different lines in this part of the world which makes even lamellaphone (although useful) artificial and imposed.

Best wishes

Keith Goddard