787: heathen, heath, and heather Feb 2, 2017

In a quite similar manner to the history of 'pagan' which you can see more about here, 'heathen' did not always have pejorative connotations. While now the word is only used to discuss certain religious groups, especially those other than Abrahamic religions and in particular Christianity, its origins with the Old English, 'hǣthen' meant someone who inhabited the rural country. The word 'heath' used to describe a bush or open, uncultivated land, comes from this same root. Likewise, the plant,'heather' appears in Old English place-names as 'hadre' but was mostly used in Scots. In the 18th century the spelling and pronunciation were changed to associate with 'heath'.

For more on religion-based swearing, see the link.