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.fk14.tu-dortmund.de/medien/ifpp/Philosophie/Beisbart/teaching/epi/epi2.pdf, 31.12.20)
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 only useful if it is simple. It cannot take into account all possible exceptions. A definition is like a logical rule (pattern): if something has the characteristics A and B, then it is a ... . Exceptions confirm the rule.
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 tu use unknown words to define a term. If an unknown word is used, it must also be defined (explained).