Dictionary.net

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

2010 - New Age Dictionary Database
By Oddity Software

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

1913 - Webster's Revised Unabridged Dictionary
By Noah Webster.