means a person who works, especially one employed to do physical or mental labor for wages

from From 'work' plus the agent suffix '-er,' the same '-er' that turns 'bake' into 'baker' and 'teach' into 'teacher.' 'Work' itself is deeply old English, descending from Old English 'weorc' and rooted in a Proto-Germanic ancestor (related to German 'Werk'), all tracing back to a Proto-Indo-European root meaning roughly 'to do' or 'to make' — the same distant family that gave us 'energy' (Greek 'ergon,' deed) and 'organ.' So a worker is, etymologically, simply a doer of deeds.