The first thing I would think of would be a betting or lottery syndicate. Taking into account the extension, I would think of a syndicate of professionals acting together. For example, a syndicate of banks lending money, a syndicate of underwriters insuring a risk or a news syndicate selling articles to the media.
This type of keyword fits .pro better than any other alternative extension but doesn't have any obvious reseller value, I think you would be looking at reg fee to $100. I paid $40 for Venture.pro and regged Enterprise.pro in 2007.
If the remaining restrictions on .pro were removed, reg fees got cut, and it was available to register through all popular registrars, business related keywords could end up being more valuable and credible in .pro than other alternative extensions.
I turned down an offer of $4,500 for Offshore.pro from a Czech company two months ago. That's up there with sale prices of Offshore.info $4,601 Sep 08 and Offshore.biz $6,500 Nov 05. I held out for $5,000 because although .info and .biz are worth more than .pro, Offshore works better with .pro than it does with .info or .biz, and is more brandable than .info and more credible than .biz.
I use Google uniques to measure the strength of association between keywords and alternative extensions, especially the ratio of the single keyword to keyword plus extension without quotes.
Offshore - 42m
Offshore Info - 6.2m
Offshore Information - 2.5m
Offshore Biz - 1.7m
Offshore Business - 2.1m
Offshore Pro - 7.2m
Offshore Professional - 8m