I have discovered that search strings that I type into the Google search text box also appear in the imdb.com text box. I believe it’s called typeahead. I entered the nonsense word kloip at Google, and sure enough there it is at imdb.com when I type the letter “k”.
Could be that your browser associates the data with the name of the text entry field. So (for example) on both sites, the “search” box is called something like Search, so your browser looks up the last dozen things you have put into a box called Search.
You may find that email addresses and your home phone number show the same effect.
Look for a setting (either in the Preferences or Options dialog) for typeahead or auto-completion or something like that.
It’s form autocompletion. The two input fields have the same name. If you’re in firefox, you can turn off the autocomplete feature in general: menu item tools -> options -> privacy, uncheck “Remember what I enter in forms and the search bar”. But then it’s not going to remember any form entries.
To eliminate that one entry, when it appears on the drop-down, just press the delete key (or possibly ctl-delete, depending on your browser).
ISTR there’s a way just to clear all auto-completes for one field (or perhaps all) without shutting off the feature, but I don’t remember what it might be.