arc cosine

noun

(ˌ)är(k)-ˈkō-ˌsīn 

variants or arccosine

plural arc cosines or arccosines

: the inverse function of the cosine

if y is the cosine of θ, then θ is the arccosine of y

—abbreviation arccos

Word History

First Known Use

circa 1884, in the meaning defined above