The root nR/nara, cognate, for example, with Latin Nero, means man.
Ish, cognate with German eigan, means to possess; Isha is master. naresha means lord of men, i.e. a king. The ending -a is dropped in most North/East modern Indian pronounciation.
ud/und/ind, cognate with the wat of water, means to flow/wet/drop, and indra has an instrumentative suffix -ra. This is the name of the rain god that rose to pre-eminence displacing the previous enveloper varuna, cognate with Uranos, as the pastorals settled in the Indian river basins. Grammarians have often tried to parse the word indra as coming from various roots like ind/inv/syand etc. connected to power, war, or conquering enemies. He was in later mythology conceived of as the king of gods, and his name was then used as a general term for pre-eminence and lord. narendra meant the foremost amongst men, i.e. a king. It was, incidentally, also the name of a meter in prosody.
naren is a development of that name in modern Indian languages like Bengali.