sesquialterate
In a ratio of 3 to 2 or 1½ times to 1.
archaic
[…]the ratio of 3 to 2, which is sesquialter, forms the symphony diapente[…]
Where it comes from
From Latin sesquialter (“one and a half times”) + -ate (adjective-forming suffix), from sesqui- (“a half and a”) + alter (“another, a second”).
Adapted from the Wiktionary entry sesquialterate (CC BY-SA 4.0).