hemiola
noun
hemi·o·la ˌhe-mē-ˈō-lə 
: a musical rhythmic alteration in which six equal notes may be heard as two groups of three or three groups of two
Word History
Etymology
Late Latin hemiolia, from Greek hēmiolia ratio of one and a half to one, from hēmi- + holos whole — more at safe
First Known Use
circa 1934, in the meaning defined above