Muddle a hundred Ptolemaic forms (10)
I believe the answer is:
complicate
'muddle' is the definition.
(I've seen this before)
'a hundred ptolemaic forms' is the wordplay.
'a hundred' becomes 'c' (roman numeral).
'forms' is an anagram indicator.
'ptolemaic' with letters rearranged gives 'omplicate'.
'c'+'omplicate'='COMPLICATE'
(Other definitions for complicate that I've seen before include "muddle" , "Make less simple" , "Make intricate" , "Make involved" .)