One of the mysteries of the English language finally explained.

# Definition of *subinvariant* in US English:

## subinvariant

### noun

MathematicsA semi-invariant of a binary quantic of arbitrary or unspecified degree. Now historical.

### adjective

MathematicsHaving the property of belonging to a finite series of subgroups each of which is a normal subgroup of the following subgroup, but not a normal subgroup of the group that is the last term of the series; designating a subgroup of such a series.

**Origin**

Late 19th century; earliest use found in James Joseph Sylvester (1814–1897), mathematician. From sub- + invariant.