The noun exciton and the adjective excitonic

The word exciton derives from the noun excitation and the suffix -on [1-3]. This suffix in exciton equals the preposition “on” and makes one think exciton is short for “the excitation is on,” but the suffix -on indicates that we are talking about a sub-nanoscale object of the wave-particle world (compare with the nouns photon, phonon, electron, proton, neutron, etc.).
An exciton is a bound electron-hole pair that originates, diffuses and dissociates inside—or at the interface of—a crystal. Direct observation of excitons is difficult [4]:

Because the [negative] electron and the positive hole have equal but opposite electrical charges, the exciton as a whole has no net electrical charge (though it transports energy). This makes excitons difficult to detect, but detection is possible by indirect means.

The adjective excitonic is used to specify materials or devices in which excitons can occur or play a critical role in their function. An excellent example are excitonic solar cells for converting light into electrical energy [5,6]. No surprise, there is a lot of excitement about excitons.

The English noun exciton in other languages
French: exciton
German: Exziton (neuter)
Italian: eccitone
Portuguese: exciton
Spanish: excitón

References
[1] www.merriam-webster.com/dictionary/Exciton
[2] www.myetymology.com/english/exciton.html
[3] www.wordnik.com/words/exciton/etymologies
[4] www.britannica.com/EBchecked/topic/197803/exciton
[5] Allon I. Hochbaum and Peidong Yang: Semiconductor Nanowires for Energy Conversion. Chem. Rev. 2010, 110, pp. 527-546 (see pages 531 to 536 on excitonic solar cells).
DOI: 10.1021/cr900075v
[6] Brian A. Gregg: The Photoconversion Mechanism of Excitonic Solar Cells. MRS Bulletin January 2005, 30, 20-22. PDF.