A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
psa 5:1Upon Nehiloth--flutes or wind instruments. The writer begs to be heard, on the ground of God's regard for His covenant-people and true worshippers as contrasted with His holy hatred to the wicked. He prays for divine guidance, on account of his watchful, malignant, and deceitful enemies; and for their destruction as being also God's enemies. At the same time he expresses his confidence that God will extend aid to His people. (Psa 5:1-12)
meditation--moanings of that half-uttered form to which deep feeling gives rise--groanings, as in Rom 8:26-27.
psa 5:2Hearken--incline the ear (Psa 10:17; compare Psa 61:2) --give close attention.
my cry--that is, for help (Psa 61:2; Jer 8:19).
my King--thus by covenant relation interested in my cause.
psa 5:3direct--literally, "set in order," as the showbread was placed or set in order (Exo 40:23).
psa 5:4For, &c.--God only regards sincere worshippers.
evil--or, "the evil man."
dwell--lodge, remain under protection.
psa 5:5foolish--vainglorious and insolent.
iniquity--especially such as denotes a negation, or defect, that is, of moral principle.
psa 5:6leasing--a lie.
the bloody . . . man--literally, "man of blood"--murderer.
psa 5:7But--as in Psa 2:6, literally, "and."
house-- (Ch1 9:23), the tabernacle.
temple--literally, "palace," applied to God's residence, the Holy of Holies (Sa1 3:3; Sa2 22:7); the inner part of the tabernacle.
toward--not in; the high priest alone was allowed to enter.
psa 5:8enemies--literally, "watchers" (Psa 27:11), hence special need of guidance.
in thy righteousness--an attribute implying faithfulness in promises as well as threatenings.
make thy way straight--that is, make the way of providence plain.
psa 5:9The wicked are not reliable because by nature they are full of wickedness, or literally, "wickednesses," of every kind (Rom 8:7).
sepulchre--a dwelling-place of corruption, emitting moral putridness.
flatter--or, "make smooth."
their tongue--speaks deceitfully.
psa 5:10Destroy--or, "condemn" them to destruction as guilty.
psa 5:11defendest--(compare Margin).
love thy name--Thy manifested perfections (Psa 9:10).
psa 5:12with favour--or, "acceptance," alluding to the favor shown to an acceptable offering and worshipper (Lev 7:18; Lev 19:7).
shield--(compare Psa 3:3).