From rahab, bluster(-er) -- proud, strength.
see HEBREW rahab
H7293. Rahab
רַ֫הַב noun [masculine] literally storm, arrogance, but only as names, v, infr; — absolute ׳ר Isaiah 30:7, רָ֑הַב Job 9:13 +; —
1 mythical sea monster (compare BartonJAOS xiv.1 (1891), 22 f.): ר ׳עֹזְרֵי Job 9:13; "" יָם 26:12; Psalm 89:11; "" תַּנִּין Isaiah 51:9.
2 emblematic name of Egypt, וּבָבֶל רַהַב Psalm 87:4; "" מצרים Isaiah 30:7.