Key massage: Of important words, you should know the exact definition.
Purdue’s Online Writing Lab says (https://owl.purdue.edu/owl/general_writing/common_writing_assignments/definitions.html, 31.12.20):
"A formal definition is based upon a concise, logical pattern that includes as much information as it can within a minimum amount of space. ... A formal definition consists of three parts:
Sokrates and Aristotle say that a definition provides the essence of a term. The essence of something is in simple words the most important of something.
Theaitetos makes a first attempt to define the word knowledge. "Socrates raises objections to this definition. ... the definition is only an enumeration; instead of getting to the essence of knowledge, it lists only instances of knowledge." (www.claus-beisbart.de/teaching/wi2005/epi/epi2.pdf, 01.08.21)
So a definition names the most important "characteristics that distinguish it" from other objects. I would put it this way: A definition names the most important conditions that must be met for an object to be labeled with the word (term). A definition is like a logical rule (pattern): if something has the characteristics A and B, then it is a ... .
A definition is only useful if it is simple. It cannot take into account all possible exceptions (exceptions confirm the rule). Exceptions do not matter if the definition is the most useful compared to other definitions.
"Only the fittest theories survive. Although it can never be legitimately said of a theory that it is true, it can hopefully be said that it is the best available …" (Chalmers, A. F. (1999). What Is This Thing Called Science? Open University Press, page 60)
A definition must satisfy another condition:
"A definition is the explanation of a previously unknown word with a combination of at least two previously known words." (Seffert , H. (1997) Einführung in die Wissenschaft. München: Beck Verlag, p. 49)
It makes no sense to use unknown words to define a term. If an unknown word is used in a definition, it has to be defined (explained) afterwards.
Definition: A definition ...
If one criterion is not met, it is not a definition.