[1] This name was popularised by the ancient German hero figure known as Reinhold von Meilan from The Dietrich Saga.

The -h- is recorded in the Dietrich von Bern legendary figure Reinholt van Meilan who was the only one spared the slaughter at Erminrich's castle due to his loyalty to Dietrich.

Hence with the addition of the -h- the etymology is interpreted as the emphatic prefix regn- with hold, apparently meaning "solemnly loyal".

[1] This name was brought to the British Isles by Viking conquerors, in the form of the Old Norse Rögnvaldr.

Cognate to English Reynold, Ronald, French Renault, Italian Rinaldo, Scandinavian Ragnvald, and Spanish Reynaldo.