dactylology

The word dactylology has a number of different meanings -- all of which generally involve the concept of using the fingers to communicate.

I'm going to tell you my definition:

Dactylology is the art, science, and study of fingerspelling.

I'm not at all satisfied with definitions that simply equate dactylology with fingerspelling as if the two words were interchangeable.  Dactylology is an "ology" that means it more than just fingerspelling but rather it involves the study of fingerspelling.

The word  "ology" means a subject of study or a branch of knowledge.
(Source:  "ology." (n.d.). In Oxford University Press's online dictionary Lexico. Retrieved March 12, 2021 from https://www.lexico.com/en/definition/ology ).

Of the various English dictionary definitions of the word "dactylology," my favorite definition (so far) is:

dactylology: The art of communicating ideas by certain movements and positions of the fingers.
(Source: http://www.etymology-dictionary.com/dactylology retrieved 12/3/2021)

Another fairly good (yet somewhat overly broad) definition is:
 

dactylology: The technique of communicating by signs made with the fingers, especially in the manual alphabets used by the deaf.

(Source: Dictionary . com which is based on the Random House Unabridged Dictionary. Accessed 12/3/2021 at https://www.dictionary.com/browse/dactylology)

My least favorite definition, according to Merriam-Webster is just:
Dactylology: finger spelling.
(Source: "dactylology." Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/dactylology. Accessed March 12, 2021.)

That definition is much too narrow and Merriam-Webster refers to fingerspelling as "finger spelling" (two words) in their definition instead of the more contemporary term "fingerspelling."  In other words, the term "finger spelling" has evolved over time to become one word.

However, for what it is worth, Merriam-Webster points out two interesting bits of information:
1. The plural form of the word dactylology is dactylologies.
 

2. The first recorded usage of the word dactylology was circa 1656. 
 

The word "circa" means approximately, about, or around.) Lexicographers (or in other words --people who make dictionaries) like to use the word "circa" before the year when discussing the first known usage of a word. "Circa 1656" is just a fancy way of saying: "We don't know the exact date but our best guess is sometime around 1656."