From rachab; enlargement, either literally (an open space, usually in a good sense), or figuratively (liberty) -- breadth, large place (room).
see HEBREW rachab
H4800. merchab
מֶרְחָב noun [masculine] broad, roomy, place; — absolute ׳מ, of pasture Hosea 4:16 (in simile); figurative of freedom from distress and anxiety 2 Samuel 22:20 = Psalm 18:20; 31:9; 118:5 (ᵑ0 construct in מֶרְחַבְיָה spacious place of Yah, i.e. extraordinarily spacious, < יָהּ יָהּ, מֶרְחָב being subject of verb); plural construct מֶרְחֲבֵיאֶֿרֶץ Habakkuk 1:6 expanses of the earth.
רחה (√ of following; meaning unknown; Late Hebrew = Biblical Hebrew; Arabic handmill (compare WetzstSiebe, ZPV xiv (1891), 4); Aramaic רִיחְיָא, ; LagBN 157 BaNB 9, 21).