Sign engaging chap's getting something to help with the crossword? (9)
I believe the answer is:
thesaurus
'something to help with the crossword?' is the definition.
(a thesaurus lists synonyms)
'sign engaging chap's' is the wordplay.
'sign' becomes 'taurus' (Taurus is an example).
'engaging' is an insertion indicator.
'chap's' becomes 'he's'.
'taurus' placed around 'hes' is 'THESAURUS'.
'getting' acts as a link.
(Other definitions for thesaurus that I've seen before include "storehouse" , "Wordbook" , "Reference work" , "Wordy gathering" , "work we may refer to" .)