1)
What is "Mezimah"?
1.
Rashi: It is the Torah.
2.
Malbim: It is the deep counsels and thoughts in Chachmah. It will guard you from stumbling in the laws of Chachmah that instruct you in matters with two ways - good and bad.
2)
What is "Tevunah"?
1.
Malbim: It distinguishes between Emes and Sheker.