The noun numismatics and the adjective numismatic came to English (via French numismatique) from Latin and Greek nomisma, meaning "coin."  Nomisma in turn derives from the Greek verb nomizein ("to use") and ultimately from the noun nomos ("custom" or "law").

The term itself first appeared in English in 1829, meaning "the study of coins and medals". It's derived from the adjective "numismatic".  This adjective, meaning "pertaining to historical coins and coinage," emerged in 1765. It was borrowed from the French word "numismatique," which had its origins in the late 1500s. 

Examples of numismatics in a sentence: 
"Numismatics, the study of coins and currency, can provide valuable insights into the history and culture of a civilization."
"The university's new museum houses a remarkable collection of numismatic artifacts." 
"Numismatic experts often specialize in specific regions or periods of coin history." 
"The ancient coin, with its unique design, is a valuable numismatic find."  
"My grandfather was a dedicated numismatist, meticulously cataloging his collection of coins." 
"The recent discovery of a hoard of Roman coins has ignited excitement in the numismatic community."  

Just the facts:

NUMISMATICS Definition & Meaning - Merriam-Webster

I'm not exactly what you would call a numismatist and I'm not numismatic, but it seems that I always end up with a pocket full of coins. 

I gather from both @Bill W and @sandrewn that numismatics is a word coined to describe people who collect coins. At least it has currency.