Ancient ewer principally covered with a precious metal (3-3)
I believe the answer is:
age-old
'ancient' is the definition.
(I've seen this before)
'ewer principally covered with a precious metal' is the wordplay.
'principally' indicates taking the first letters.
'covered with' is an insertion indicator.
'precious metal' becomes 'gold' (gold is a precious metal).
The first letter of 'ewer' is 'e'.
'a'+'gold'='agold'
'e' going into 'agold' is 'AGE-OLD'.
(Other definitions for age-old that I've seen before include "Hallowed by antiquity" , "Having been around for many years" , "Lasting from times long ago" , "Extremely ancient" , "Having existed for a very long time" .)