hootenanny
Concise Oxford English Dictionary © 2008 Oxford University Press:
hootenanny /ˈhuːt(ə)ˌnani/
▶noun (pl. hootenannies) informal, chiefly US an informal gathering with folk music.
– origin 1920s (orig. US, denoting a ‘thingummy’): of unknown origin.
'hootenanny' also found in these Oxford entries:

