Hotel put columns up inside - there's eight of them! (7)
I believe the answer is:
octuple
'eight of them' is the definition.
I can't judge whether this definition defines the answer.
'hotel put columns up inside' is the wordplay.
'inside' indicates a hidden word.
'up' says the letters should be written backwards (in down clue: letters go upwards).
'elputco' is hidden within 'hotel put columns'.
'elputco' backwards is 'OCTUPLE'.
'there's' is the link.
Can you help me to learn more?
(Other definitions for octuple that I've seen before include "Eightfold" , "more than seven times" , "Couplet (anag)" , "multiply by eight" , "8 times" .)