Select the clip you want to remove the keyword from, and open the Keyword HUD (cmd+K) - delete the keyword from there, and your clip will disappear from that collection while retaining your other keywords.
If I select the shot in the main event no problem but if I select the shot within a keyword collection it deletes everything but of course it is removing itself from the keyword collection. Should have figured that. I was thinking it was deleting all the keywords but in the main event they are still there.
Every now and then I still get a bout of confusedness.