Understood vase to be short (8)
I believe the answer is:
taciturn
'short' is the definition.
(thesaurus)
'understood vase' is the wordplay.
'understood' becomes 'tacit' (I've seen this before).
'vase' becomes 'urn' (both can mean a container).
'tacit'+'urn'='TACITURN'
'to be' is the link.
(Other definitions for taciturn that I've seen before include "Talking little" , "Reserved and uncommunicative" , "Reserved, saying little" , "Disinclined towards conversation" , "Untalkative" .)