Q. What does "sostenente" mean in musical terms? Are there any musical works on CD at the library that illustrate examples of this?

Sostenente is a form of the Italian verb sostenere, meaning, in musical terms, to sustain.  It seems to be used primarly as the name of a type of musical instrument, the sostenente piano. 

Here's part of an article from Piano: and Encyclopedia:

Sostenente (or sostinente) piano is the name given to keyboard instruments on which the duration of sounds is artificially lengthened.  This can be done by (1) an endless bow, (2) compressed air, (3) repeated and quick striking of HAMMERS, (4) free sounding reeds, (5) or electric and/or electronic devices. The name sostenente is derived from the sostenente piano invented by Henry Robert Mott of Brighton (1817). A sostenente piano is by no means exclusively a piano.

The Hohner Company, in 1960, produced a version of the sostenente piano in the form of its Clavinet.  The Clavinet was widely used in rock bands from the late 60s on through the present time.  Billy Preston used it on his hits "Space Race" and "Will it Go Round in Circles"; Herbie Hancock used it throughout the HeadHunters album.  Stevie Wonder famously used the Clavinet on "Superstition" and "Higher Ground".  Other bands to use the clavinet include Led Zepplin, Vetiver, Stereolab, Mr. Bungle, the Rolling Stones, and the Red Hot Chili Peppers.