word vs arcanum

word and arcanum both are nouns.

Word	Noun	Adjective	Verb	Adverb
word	Yes	No	Yes	No
arcanum	Yes	No	No	No

As nouns, arcanum is a hypernym of word; that is, arcanum is a word with a broader meaning than word:

Other hypernyms of word include secret, positive identification.

word (noun)	arcanum (noun)
a unit of language that native speakers can identify	information known only to a special group
a promise
information about recent and important events
a brief statement
an exchange of views on some topic
a secret word or phrase known only to a restricted group
a verbal command for action
a string of bits stored in computer memory

word (verb)	arcanum (verb)
put into words or an expression