A person or tool that marks outlines, boundaries, or precise descriptions of something.
From 'delineate' plus the suffix '-or' (or '-er'), which designates a person or instrument that performs an action. This follows the standard pattern seen in words like 'creator' or 'actor.'
Road workers use plastic 'delineators' (the orange and white reflective posts) to mark lane boundaries—they're literally 'things that delineate' where drivers should go, proving the word works perfectly for both people and objects.
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