Laborer is the American spelling of labourer. A laborer is a person whose job is physical work — digging, carrying, building, packing — rather than sitting at a desk. In American English this is the ordinary dictionary word; British English writes labourer. You will see it in job notices and news (“farm laborers,” “day laborers”). Though actually, in careful everyday talk many people now just say worker and then name the work, because laborer can sound official or a little old. It names the person who does the labour, not how hard or slow the task feels (that is laborious), and not the person who hires them (that is the employer). It is also not someone who works in a laboratory.