Try the Ultralingua API

The Ultralingua Application Programming Interface (ULAPI) lets you add sophisticated language features to your applications. These demonstrations use the REST form of ULAPI. The same features are available in the iOS, C++, and Python ULAPI interfaces as well.

There's more than this to ULAPI. See the feature summary, the ULAPI REST Documentation, and the ULAPI C++ Documentation for details.

Word lookup / translation

to

Plurals

Stemming (finding root words)

Verb conjugation

Number translation