According to general belief, the name of Coromandel coast is derived from the Tamil “ Cholamandalam” or “land of Cholas”. Wikipedia says:
The land of the Chola dynasty was called Cholamandalam in Tamil, literally translated as The realm of the Cholas, from which Coromandel is derived. Another research shows that the coast along the Chola country was called Cholamandalam which was later corrupted to Coromandel by the Europeans. According to The Periplus of the Erythræan Sea by Wilfred Harvey Schoff, the Chola coast was derived from the native Tamil name Chola-mandalam, from which the Portuguese derived our modern word Coromandel.
“The CarnaticChronology” written by Charles Philip Brown and published in 1868 however provides the following explanation (page 68) digging into old records of the Dutch, dated 1623.
"Coromandel" is first named under this date in the Dutch accounts of India. Coromandel was the Dutch spelling of Kurumanil, that is, "Blacksand," a fishing village a little north of Madras. Among Europeans the entire coast has acquired this name, which also has been changed by pedantry into Kuru-mandalam (land of the Kurus; which it never was) The name Coromandel as denoting a region is wholly unknown to the natives.
The latter explanation sounds more logical to me.