This is not completely a Naval term, but it is still interesting none the less. In Medieval and Colonial times, the job of the Apprentice was to hold a candle over the Master's hands while he worked, if it was dark or late in the evening. The Apprentice was to observe closely to move the candle as required and to watch and learn how the master worked. This term soon came to be applied to an apprentice so lazy or incompetent that he couldn't even be trusted with this simple task.

I know that every single one of us knows a few people that fall into this category, but please keep their names to yourselves.