Brand new means never used before. A brand new car, brand new out of the box, brand new to the job.
The brand in it is a burning, from something newly forged and still glowing, which is the same brand as in branding iron. Of a person it means completely inexperienced rather than young.
1adjectivebrand newNever used before.
“He saved for years and finally bought a brand new car straight from the showroom.”
brand new is a quality.
Brand plus new, from something newly taken from the fire, with brand meaning a burning.
From brand + new, implying something that is newly forged (first citation 1570; compare fire-new (“fresh from the fire, brand-new”)). Alternatively, and less likely from brand as in a branding iron (i.e. newly-branded). The first element of the variant bran new, with the post nasal stop deletion common to English (compare the common pronunciation (outside Britain) of hunting as hunning), is claimed to be from bran as if from cases where new items were supposedly “packaged up with unwanted grain (bran) in the 18th century to protect the objects during transit” (source unknown). Both variants are well attested.
Etymology from Wiktionary, CC BY-SA
Practised in Everyday Adjectives