Rom (pl. Roma) - male member of the group, "Romani husband"
Romni (pl. Romnja) - female member of the group, "Romani wife"
Most probably, as in India, where the caste name is primary and its use to designate marital status is secondary, the terms "rom" and "romni" originally denote the ethnonym, and the meaning "husband" and "wife" are a secondary extension. In transcriptions the difference is sometimes marked by a capital letter - "Rom" - for the ethnonym in difference to "rom" for the marital status (same with "Romni" vs. "romni"). The basic distinction of "rom" as "Romani husband" versus "gadžo" as "non-Romani husband" is not applied strictly, maybe it never was (likewise with "romni" and "gadži"). Thus Roma may refer to the husband in a family of gadže as "rom", if the two families are close and well acquainted.
Source and further reading:
ROMBASE © by Milena Hübschmannová 2003
Roma in: ROMANE THANA
Roma, Romni (Sg. m. romni, Pl. next to roma also rom; Sg. f. romni, Pl. romnija; translated: "Mensch", "man") designates all members of the Romanes-speaking groups with a Romanes word. In 1971, the first World Congress of the international civil rights movement of the Roma in London decided to replace the foreign term "Gypsy", which had previously been customary in English-speaking countries, as the overall term for members of the minority with the proper term "Roma". On the recommendation of its Language Commission, the International Roma Union (IRU) adopted the resolution. The second international umbrella organisation of Roma organisations, the Roma National Congress (RNC), today also uses the term "Roma" as a collective term for the minority divided into numerous sub-groups (such as Spanish "Calé", Hungarian "Gabor", Eastern European, Scandinavian, American "Kalderash", "Lalleri", "Lovara", "Sinti").
(c) Karola Fings/Ulrich F. Opfermann