What is "Navar"?
Rashi (Tehilim 18:27): It is trustworthy.
Radak: Navar is like "k'Vor Yadai" (verse 21).
Metzudas David: It is clear, and clean [from sin].
Who is an Ikesh?
Rashi: This refers to Pharaoh.
Mahari Kara: It is the Resha'im of every generation, who make their way crooked in front of You.
What is the meaning of "Titapal"?
Rashi: It is an expression of Niftal and crooked. In Tehilim (28:27) it says Tispatal. Radak - the root is Tipatal. The Pei and Tav were switched, to make the word similar to Titavar and Titamam (verse 26). You should bring upon him like his crooked way. This is like "Im la'Letzim Hu Yalitz" (Mishlei 3:34) - He brings on them to stumble in their frivolity.
Is it proper to be crooked with Resha'im?
Mesilas Yesharim (Perek 11): If someone asks you for counsel, if his intent is for evil, it is a Mitzvah to deceive him. 1
It is a Heter; every Heter has its price. Yakov used this Heter with Lavan (Yakov pretended to trust him to give Rachel, and did not tell Lavan that he has Simanim to guard against trickery), and it did not help him at all! (Heard from R' C. T. Fogel, in the name of R' Yechezkel Levenstein.)
We find that Chushai ha'Archi deceived Avshalom, and pretended that he is trying to help him (and covertly sent to tell David how to save himself - Shmuel II, 17:15), for Avshalom was ready to kill David. (PF)
