Boring tellers avoid silver-plated plastic (5)
I believe the answer is:
vapid
'boring' is the definition.
(I've seen this before)
'tellers avoid silver-plated plastic' is the wordplay.
'avoid' is a deletion indicator.
'plastic' is an anagram indicator (plastic can mean easily moulded).
'silver'+'plated'='silverplated'
'silverplated' with 'tellers' taken out is 'ivpad'.
'ivpad' with letters rearranged gives 'VAPID'.
(Other definitions for vapid that I've seen before include "Insipid - lacking significance" , "Boring, flat" , "Dull - uninteresting" , "Dull and boring" , "Insipid, empty" .)