co-defendant vs defendant

co-defendant and defendant both are nouns.

Word	Noun	Adjective	Verb	Adverb
co-defendant	Yes	No	No	No
defendant	Yes	No	No	No

As nouns, defendant is a hypernym of co-defendant; that is, defendant is a word with a broader meaning than co-defendant:

co-defendant: a defendant who has been joined together with one or more other defendants in a single action
defendant: a person or institution against whom an action is brought in a court of law; the person being sued or accused

Other hypernyms of co-defendant include suspect.

co-defendant (noun)	defendant (noun)
a defendant who has been joined together with one or more other defendants in a single action	a person or institution against whom an action is brought in a court of law; the person being sued or accused