Pete Seeger appears to have been the thread into common vernacular.

We referred to ours as "Nannyhoots" (the "Nitty Gritty Dirt Band's" spontaneous infusion (they requested "musical housing for the night" each band member stayed at a different individual's abode and jammed with residents until nearly dawn) into the local community - previously related in another thread - created a fusion of energy that lasted years.))

J.E. Lighter's RHD Am. Slang
[orig. unkn.] 1. a comparatively small ting whose name is unkown or forgotten; a shatchamacallit; gadget; 9hence, rarely an inconsequential peron. (Lighter references 1929 to 1977)

2. a. any sort of informal social event or party 1940.

b. a performance of folk music, esp. by a number of artists with a degree of audience paricipation. Now colloq.

1957 P. Seeger om Sing Out! (Winter) 34: Another took a tapre recorder with her and set up amall hootenannies in courtry stores, and recorded the singing. 1960 Seeger & McColl Singing Island The kind of songs which are delighting audiences at concerts and hootenannies up and down Great Britain.