Student or Learner
"Upright" can mean either honorable or vertical; "horizontal" and "supine" are both antonyms of upright.
Do you confirm this claim?( Came from 501 Synonym & Antonym Questions book)
As always, it depends on the context.
'The mayor is an honorable man, but his predecessor was horizontal'. Does that make sense to you?
Does the author of the book warn you that synonyms and antonyms are rarely completely interchangeable and must be considered in the context in which they are used?