accessorius
noun
ac·ces·so·ri·us
| \ ˌak-sə-ˈsōr-ē-əs, -ˈsȯr-
\
\
plural accessorii\ -ē-ˌī, -ē-ˌē
\
\
Medical Definition of accessorius
1
: a muscle reinforcing the action of another
2
: accessory nerve