Several etymologies have been suggested: ▪ Arab lexicographers derive it from ↗√RḤB ‘ample, wide’ as a vn. or n.loc. »You say marḥaban and marḥaban bi-ka meaning ‘Thou hast come to, or found, ampleness, spaciousness, or roominess’, or ‘alight you, or abide you in ampleness, etc.’, for such we have for thee, the word being put in the acc. because of a verb understood; or ‘thou hast alighted in an ample […] space’, ‘welcome to ampleness [etc.]’« (Lane iii 1867). – Cf. Hbr märḥāb ‘broad, roomy place’, which is also used figuratively »of freedom from distress and anxiety« (BDB1906).
▪ Another theory traces it back to Syr mār ḥūbā ‘The Lord is (full of) love’, allegedly a greating among Aramaic-speaking Christians.
▪ A third explanation sees it as an Arabized form of Pers mehr-bān, an adj. signifying (accord. to Steingass) ‘benevolent, benficient, kind, affectionate, friendly, compassionate, favouring, loving; […] a friend’.