In that place (5)
(Other definitions for thorn that I've seen before include "tip of R [ROSE]" , "Sharp point on, eg, rose" , "Sharp-pointed stem-tip" , "Pointed growth" , "Prickly plant" .)
'in that place' is the definition.
(over there)
This is all the clue.
(Other definitions for there that I've seen before include "Word of comfort" , "in that case" , "In that location" , "Yonder" , "Present" .)
'in that place' is the definition.
This is the entire clue.
(Other definitions for thereat that I've seen before include "At that point" , "At that place" , "On account of that" , "Theatre (anag)" .)