Strangely variable opening of draft of part of speech (9)
I believe the answer is:
adverbial
'part of speech' is the definition.
(thesaurus)
'strangely variable opening of draft' is the wordplay.
'strangely' indicates an anagram.
'opening of' indicates taking the first letters.
The first letter of 'draft' is 'd'.
'variable'+'d'='variabled'
'variabled' with letters rearranged gives 'ADVERBIAL'.
'of' is the link.
(Other definitions for adverbial that I've seen before include "modifying another word?" , "Relating to a modifying word" .)