(n.) A hole through which a man may descend or creep into a drain, sewer, steam boiler, parts of machinery, etc., for cleaning or repairing.

air hole armhole blowhole bullet-hole bunghole cringle deadeye eye eyelet gasket grommet guide keyhole knothole loop loophole mousehole peephole pigeonhole pinhole placket placket hole porthole punch-hole spiracle tap vent venthole