Etymology
The former name Bombay had its origins in the 16th century when the Portuguese arrived in the area and called it by various names, which finally took the written form Bombaim, still common in current Portuguese use. After the British gained possession in the 17th century, it was anglicised to Bombay, although it was known as Mumbai or Mambai to Marathi and Gujarati-speakers, and as Bambai in Hindi, Urdu. A widespread explanation of the origin of the traditional English name Bombay holds that it was derived from a Portuguese name meaning "good bay".This is based on the fact that bom (masc.) is Portuguese for "good" whereas the English word "bay" is similar to the Portuguese baía (fem., bahia in old spelling). The normal Portuguese rendering of "good bay" would have been boa bahia rather than the grammatically incorrect bom bahia. However, it is possible to find the form baim (masc.) for "little bay" in sixteenth-century Portuguese.

Other sources have a different origin for the Portuguese toponym Bombaim. José Pedro Machado's Dicionário Onomástico Etimológico da Língua Portuguesa ("Portuguese Dictionary of Onomastics and Etymology") mentions what is probably the first Portuguese reference to the place, dated from 1516, as Benamajambu or Tena-Maiambu,pointing out that "MAIAMBU"' seems to refer to Mumba-Devi, the Hindu goddess after which the place is named in Marathi (Mumbai). In that same century, the spelling seems to have evolved to Mombayn (1525)and then Mombaim (1563).The final form Bombaim appears later in the 16th century, as recorded by Gaspar Correia in his Lendas da Índia ("Legends of India").J.P. Machado seems to reject the "Bom Bahia" hypothesis, asserting that Portuguese records mentioning the presence of a bay at the place led the English to assume that the noun (bahia, "bay") was an integral part of the Portuguese toponym, hence the English version Bombay, adapted from Portuguese.