Define and date key part of vault (English) (8)
I believe the answer is:
describe
'define' is the definition.
(thesaurus)
'date key part of vault english' is the wordplay.
'date' becomes 'd' (common abbreviation eg in DOB, date of birth).
'key' becomes 'esc' ('Escape' key on a computer keyboard).
'part of vault' becomes 'rib' (architectural term).
'english' becomes 'e' (abbreviation).
'd'+'esc'+'rib'+'e'='DESCRIBE'
'and' acts as a link.
(Other definitions for describe that I've seen before include "provide an account" , "Draw (a geometrical figure)" , "Report in detail" , "Delineate" , "Paint in words" .)