Not saying much, showing discretion about one vase (8)
I believe the answer is:
taciturn
'not saying much' is the definition.
(I've seen this before)
'discretion about one vase' is the wordplay.
'discretion' becomes 'tact' (I've seen this before).
'about' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'vase' becomes 'urn' (urn is a kind of vase).
'tact' enclosing 'i' is 'tacit'.
'tacit'+'urn'='TACITURN'
'showing' is the link.
(Other definitions for taciturn that I've seen before include "Without saying much" , "Uncommunicative, of few words" , "Reticent" , "Tight-lipped" , "Disinclined towards conversation" .)