Guillotined, peak figure (5)
I believe the answer is:
eight
'figure' is the definition.
(I know that eight is a type of figure)
'guillotined peak' is the wordplay.
'guillotined' means to remove the first letter.
'peak' becomes 'height' (synonyms).
'height' with its first letter taken away is 'EIGHT'.
(Other definitions for eight that I've seen before include "destroyed [IN 8A] here!" , "Mathematical cube" , "Number for a racing boat" , "Set of rowers" , "Where arrogance is needed" .)