"___ at a time" (3)
I believe the answer is:
one
(Other definitions for one that I've seen before include "I can mean this" , "This is singular" , "Single, unitary" , "If upper-class, perhaps I" , "Single, sole" .)
I believe the answer is:
one
(Other definitions for one that I've seen before include "I can mean this" , "This is singular" , "Single, unitary" , "If upper-class, perhaps I" , "Single, sole" .)