That is, I have created a Twitter list with some 100 members and would like to search for a particular word within all users of the list.
Use the search string:
So for instance:
Very similar to the answer I literally just gave at https://webapps.stackexchange.com/a/45443/10707, but it's still relevent....
http://www.tweepi.com/ let's you see all of the members of a public list and, you can choose to see their bios in the table as well - more importantly you can filter on text in the bio - the screenshot shows me filtering on the keyword 'phd'