Block terribly vain liberal (5)
I believe the answer is:
anvil
'block' is the definition.
(I know that anvil is a type of block)
'terribly vain liberal' is the wordplay.
'terribly' is an anagram indicator.
'liberal' becomes 'l' (abbreviation).
'vain' anagrammed gives 'anvi'.
'anvi'+'l'='ANVIL'
(Other definitions for anvil that I've seen before include "One getting hammered regularly" , "Smith's heavy iron block" , "bit off one's ear" , "Block for metalworking" , "Block on which metal can be hammered" .)