Model sleek and tall, almost gaunt (8)
I believe the answer is:
skeletal
'gaunt' is the definition.
(I know that gaunt can be written as skeletal)
'model sleek and tall almost' is the wordplay.
'model' indicates anagramming the letters.
'and' says to put letters next to each other.
'almost' means to remove the last letter (most of the word but not all of it).
'tall' with its final letter taken off is 'tal'.
'sleek' with letters rearranged gives 'skele'.
'skele'+'tal'='SKELETAL'
(Other definitions for skeletal that I've seen before include "reduced to a minimum" , "Very thin, emaciated" , "Consisting of bones" , "Comprising just the bare bones" , "pinched" .)