melodeon
Concise Oxford English Dictionary © 2008 Oxford University Press:
melodeon /mɪˈləʊdɪən/ (also melodion)
▶noun
- 1 a small accordion of German origin, played especially by folk musicians.
- 2 a small organ popular in the 19th century, similar to the harmonium.
– origin C19: prob. from melody, on the pattern of accordion; sense 2 is an alt. of earlier melodium.
'melodeon' also found in these Oxford entries:

