That one or this one (6)
I believe the answer is:
either
I believe this clue is a double definition.
'that one' is the first definition.
(thesaurus)
'this one' is the second definition.
(thesaurus)
(Other definitions for either that I've seen before include "Each of two; moreover" , "Word indicating the following alternatives" , "Her tie (anag.)" , "offered a choice" , "could be one of two" .)