This is the 9619th most frequent Spanish word.
archi
A prefix meaning "super," "ultra," or "chief."
Here, 'archi' acts as a prefix to intensify the adjective 'conocido', suggesting that someone is extremely well-known.
Él es archiconocido en esta ciudad por su buen trabajo.
He is very well-known in this city for his good work.
In this case, 'archi' is used to intensify the meaning of 'sabía', signifying a complete or absolute certainty regarding knowledge.
Yo archisabía la respuesta al problema antes de que lo dijeras.
I absolutely knew the answer to the problem before you said it.
Here, 'archi' serves as a prefix to denote an ultimate or intense level of enmity, shaping the term 'archienemigos' to mean more than just enemies—almost opposites or nemeses.