Smarting is the present participle of the verb smart, from Old English smeortan ('to be painful, sting'), from Proto-Germanic *smertaną, from Proto-Indo-European *smerd- ('to bite, sting, hurt'). The historical chain includes Old English smeortan, Proto-Germanic *smertaną, and Proto-Indo-European *smerd-. Older glosses in the chain include "to be painful, sting" and "to bite, sting, hurt", which help explain the semantic range of the modern word. Morphologically, smarting is best read as borrowing, yielding an English adjective shaped by both form history and later usage. In current English it functions as an adjective, with the sense "causing or feeling a sharp stinging pain". related forms include smart. The result is an English adjective whose etymology preserves the older forms while supporting the word's specialized modern meaning.