There are many opinions about the origin of the word ‘India’. But Sankrant Sanu gives the most possible answer of this question.
According to him, first, the word ‘Hindu’ is derived from the Rigvedic river named ‘Sindhu’. Then, Sankrat says that, some foreigner languages often omit the pronunciation of ‘h’. Thus, they pronounce ‘Hindu’, by skipping ‘h’, as ‘Indu’. ‘H’ is silent here.
It is like this the word ‘Sindhu’ gradually become the ‘Indus’ and then India. Names like ‘Inde’, ‘Indica’, India are attested in several foreign texts.