oc ‧ tave /ˈɒktəv, ˈɒktɪv, -teɪv $ ˈɑːk-/ BrE AmE noun [countable]
[ Date: 1300-1400 ; Language: Medieval Latin ; Origin: octava , from Latin octo 'eight' ; because there are eight notes in the range ]
a) the range of musical notes between the first note of a ↑ scale and the last one
b) the first and last notes of a musical ↑ scale played together