In science, the prefix thermo- refers to "heat" or "hot" a combination of the Greek words thermós (hot) + thérmé (heat). [1] The use of the prefix, as in thermo-magnetism (1824), thermo-stat (1831), thermo-electricity (1834), or thermo-chemistry (1840), etc. dates back to at least the 1820s if not before. [2]

History
Possibly, the earliest use of the prefix thermo- was the term “thermometer” (1663) from the French thermomètre (1624), coined by Jesuit Father Leuréchon from Greek thermos "hot" + metron "measure". [3]

Thermo-dynamics
The term was first used in a thermodynamical-sense in 1849 by Scottish physicist William Thomson who referred to a "perfect thermo-dynamic engine", in reference to the ideal Carnot engine, having no irreversibility, described by French physicist Sadi Carnot in 1824.

See also
● -dynamic

References
1. Random House Unabridged Dictionary, © Random House, Inc. 2006.
2. (a) Traill, Thomas Stewart. (1824). On Thermo-magnetism. Printed for A. Constable, 6 pages.
(b) Thermostat (1831) – Online Etymology Dictionary, 2001 by Douglas Harper
(c) Meyer, Ernst von. (1898). A History of Chemistry from the Earliest Times to the Present Day. (pg. 507 cites that Ostwald refers to G. H. Hess, and his 1840 work, "Constanz der Warmesummen", as being the founder of thermo-chemistry). The Macmillan Company.
3. Thermometer (1663) – Online Etymology Dictionary, 2001 by Douglas Harper.