The word is 'List'.
As far as I can make out,the name preceding the word List is that of the 'Master' and the names that follow are those of their household, slaves or servants.
So, for the extracts in your question, we have:
Mary Clay's List
John Sturdivant's List
Obadiah Smith's List
The Library of Virginia has published a series of Research Notes, which I've found very helpful over the years. Research Notes Number 17 describes Colonial Tithables. Every head of household or master was required to submit a list of those liable for tithes. Note that after 1723,
In addition to their tithable lists, all masters were required to list the names of every person between the ages of ten and sixteen “for whom any benefit of tending Tobacco is allowed by this Act.” In tithable lists, masters were required to distinguish which persons were primarily employed in the cultivation of tobacco.
There are also linked pages on the associated legislative history, and a case study that you might find useful.