In geometry, a **demienneract** or **9-demicube** is a uniform 9-polytope, constructed from the 9-cube, with alternated vertices truncated. It is part of a dimensionally infinite family of uniform polytopes called demihypercubes.

E. L. Elte identified it in 1912 as a semiregular polytope, labeling it as HM_{9} for a 9-dimensional *half measure* polytope.

Coxeter named this polytope as **1**_{61} from its Coxeter diagram, with a ring on one of the 1-length branches, and Schläfli symbol
{
3
3
,
3
,
3
,
3
,
3
,
3
3
}
or {3,3^{6,1}}.

Cartesian coordinates for the vertices of a demienneract centered at the origin are alternate halves of the enneract:

(±1,±1,±1,±1,±1,±1,±1,±1,±1)

with an odd number of plus signs.