What is the meaning of this word?

I heard it from a game. Tsukae zu. What is the meaning of this "zu" ? Tsukae's meaning is "to use, to serve" etc.
Thank you for your response.

"zu" means "not" or can't. Tsukaezu means you can't use it.

"Tsukae zu" by itself would be interpreted as meaning "you can't use it",
but with the subject used along it, the meaning would be different.
Moreover, this usage of "zu" as negation is rather classical and formal one.

I am reminded of a Japanese classical saying "Bushi wa nikun ni tukaezu",
or "A samurai would not serve two lords" in English,
and shows the loyalty of samurai which would be taken to be stubbornness nowadays.

"tsukaezu" in modern Japanese would be "tsukaenai" - "-zu" and "-nai" are negative ending for verbs.

When it comes to the meaning, "tsukaezu" (or "tsukaenai") may be:
(1) negative form of the verb "tsukaeru," to serve (a master), so the meaning would be "does not serve,"
or
(2) negative form of the "can do" form ("tsukaeru") of the verb "tsukau," meaning to use, so the meaning would be "cannot use," or "cannot be used."