Origins
Blend is a Viking word. It entered English through Old Norse blanda meaning 'to mix', likely reinforced by the native Old English blandan with the same meaning. When Norse-speaking settlers occupied the Danelaw in the 9th and 10th centuries, their vocabulary merged with English — and blend is a product of that merger.
The Proto-Germanic ancestor *blandaną carried connotations of making something cloudy or turbid. To blend liquids was to stir them until neither could be distinguished. This sense of loss through mixing persisted: in Middle English, blenden could mean 'to deceive' — to blend truth with falsehood until neither was recognisable.
The Scandinavian cognates survive intact. Icelandic blanda, Swedish blanda, and Danish blande all mean 'to mix'. The consistency across a thousand years of separate development shows how stable this word has been.
Scientific Usage
In the 20th century, blend gained a technical meaning in linguistics. A blend word — also called a portmanteau — fuses two words into one: brunch (breakfast + lunch), smog (smoke + fog), motel (motor + hotel). The term is fitting: just as blended liquids lose their individual identities, blended words absorb their parents.
The kitchen appliance called a blender, first marketed in the 1930s, brought the word into daily domestic use and cemented its association with pulverising things into smoothness.