In fact since the Pythagoreans [1] where the monad comes first and after the dyad and after the numbers and so on. It also was the term for unicellular organism before this was coined.
Monadic was an adjective used in logic before the 20th century, using the noun dervied by the greek root monas which gave monad and monadic (and the same with dyad, dyadic).
If I take for right what is on the french [2] and english pages [3] of wikipedia about the terminology history of the monad words its usages seems to date to around the 70 when Saunders Mac Lane named it in reference to the philosophical term.
I feels some times people tend to forget how interconnected is and was mathematics and philosophy and how term from philosophy were used in a mathematical context based on their philosophical definition.
Monadic was an adjective used in logic before the 20th century, using the noun dervied by the greek root monas which gave monad and monadic (and the same with dyad, dyadic).
If I take for right what is on the french [2] and english pages [3] of wikipedia about the terminology history of the monad words its usages seems to date to around the 70 when Saunders Mac Lane named it in reference to the philosophical term.
I feels some times people tend to forget how interconnected is and was mathematics and philosophy and how term from philosophy were used in a mathematical context based on their philosophical definition.
[1] https://en.wikipedia.org/wiki/Monad_(philosophy)
[2] https://fr.wikipedia.org/wiki/Monade_(th%C3%A9orie_des_cat%C...
[3] https://en.wikipedia.org/wiki/Monad_(category_theory)#Termin...