Thou hast broken Rahab in pieces - Margin, "Egypt." See the notes at Psalm 87:4. The reference is to the exodus of the Hebrew people, when he destroyed the power of Egypt.
As one that is slain - Slain on the field of battle; as a man pierced through with a sword or spear.
Thou hast scattered thine enemies - At the time referred to, in Egypt; and at other times, when the enemies of God and of his people had been discomfited.
With thy strong arm - Margin, as in Hebrew, the arm of thy strength. That is, by his power - the arm being the symbol of power. See the notes at Psalm 77:15. Compare Deuteronomy 5:15; Deuteronomy 7:8, Deuteronomy 7:19, et al.

Thou hast broken Rahab - Thou hast destroyed the power of Egypt, having overthrown the king and its people when they endeavored to prevent thy people from regaining their liberty.
As one that is slain - The whole clause in the original is, אתה דכאת כחלל רהב attah dikkitha kechalal Rahab, "Thou, like a hero, hast broken down Egypt." Dr. Kennicott has largely proved that חלל chalal, which we render wounded, slain, etc., means a soldier, warrior, hero; and it is certain that this sense agrees better with it than the other in a great number of places. Mr. Berlin translates, Tu contrivisti ut cadaver Aegyptum; "Thou hast bruised down Egypt like a dead carcass." The whole strength of Egypt could avail nothing against thee. Thou didst trample them down as easily as if they had all been dead carcasses.

Thou hast broken Rahab in pieces, as one that is slain,.... Or Egypt, as in Psalm 87:4 or the Egyptians, and particularly Pharaoh their king; so the Targum explains it,
"Rahab or the proud one, this is Pharaoh the wicked;''
who and his people were broken to pieces by the plagues that were brought upon them, especially when all their firstborn were slain; and he and his host were broke in pieces at the Red sea, and were seen by the Israelites on the shore, all dead men; and this was done as easily by the Lord, as one slain with the sword, as a dead carcass which has no life, power, and strength to defend itself, may be trampled upon, crushed, bruised, and broken to pieces, by a living man. All this may be an emblem of the Lord's breaking in pieces the proud and insolent one Satan, as Rahab signifies; of his breaking his head, destroying his works, and spoiling his principalities and powers; and indeed of his destruction of every proud and haughty sinner, that says, Pharaoh like, who is the Lord, that I should obey him? and of every vain boaster, and self-righteous person, that trusts in his own righteousness, and will not submit to the righteousness of Christ; and particularly of mystical Egypt, the proud beast of Rome, antichrist, who sits in the temple of God as if he was God, showing himself to be so, blaspheming God, his name, his tabernacle, and his saints; who will be broken to shivers as a potter's vessel, when the vials of God's wrath are poured out, and at and by the coming of Christ:
thou hast scattered thine enemies with thy strong arm; as the Egyptians were in the Red sea, by the waves of it, and cast upon the shore by them; and as the Amorites were by Moses, and the Canaanites by Joshua; which instances may be here referred unto; see Numbers 10:35 these are further proofs of the power and strength of the Lord, Job 40:9.

Rhahab - Egypt.