http://www.dpaonthenet.net/products/September2000/prod_mechtext01.html

Apparently (subject to further googling) "plummer block" is a general (not nautical) term for a kind of housing for bearings.

"The quality of the housing in which a bearing is secured has a significant effect on the performance and life expectancy of the bearing. Even bearings of the highest quality, correctly specified and diligently lubricated can fail prematurely if the housing is not concentric or if it has been over-tightened. The development of an easy-to-install and flexible bearing housing solution was first addressed many years ago with the introduction of what is often referred to as a split plummer block."