The sadness of a way that's so crooked (6)
I believe the answer is:
pathos
'the sadness' is the definition.
(thesaurus)
'a way that's so crooked' is the wordplay.
'a way' becomes 'path' ('path' can be a synonym of 'way').
'that's' means one lot of letters go next to another.
'crooked' is an anagram indicator (a crooked or disrupted version of the letters).
'so' anagrammed gives 'os'.
'path'+'os'='PATHOS'
'of' is the link.
(Other definitions for pathos that I've seen before include "Pitifulness" , "Quality arousing pity" , "Pitiful quality" , "Quality inspiring pity" , "pitiful feeling" .)