The word 'tar' is an ancient substance, and its name has a straightforward lineage. It originates from the Old English word 'teoru', which itself comes from the Proto-Germanic 'terwą', meaning resin or tar. This Germanic root is likely related to the Proto-Indo-European 'deru-', meaning tree or wood, highlighting the substance's origin as a product derived from wood. The modern verb 'to tar' means to coat with this dark, viscous material, and 'tarred' simply denotes the state of having undergone that action, preserving the core material's name without complex morphological segmentation.

The word 'tarred' is a suffixed form of the simplex noun/verb 'tar'. The suffix '-ed' is of Old English origin, used here to form the past tense and past participle of a verb or an adjective meaning "having the characteristic of".