Uh, pretty much a mis-placed tradition, according to the writings of people more knowlegable than I am. Check out the postings of Peter Goldsbury and Josh Reyer, here and on aikido journal.
The idea of "bu" meaning "stop the halberd" or its various permutations is not linquistically accurate from my understanding, but the use of that idea is in fact fairly old in Japan and while it may not be linquistically accurate, it is something that has colored the Japanese view of the character for quite a long time. Within the ryu I am a member of, one of the core teachings of the entire tradition is based off of a permutation hoko/todomeru idea. We have densho dating back to the 1600's surviving that talk about this teaching in great detail.