Tiresomely plug new gold layer (2,7)
I believe the answer is:
ad nauseam
'tiresomely' is the definition.
Both the answer and definition are adverbs. Perhaps they are linked in a way I don't understand?
'plug new gold layer' is the wordplay.
'plug' becomes 'ad' (as in plugging a product).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'layer' becomes 'seam' (seam is a kind of layer).
'ad'+'n'+'au'+'seam'='AD NAUSEAM'
Can you help me to learn more?
(Other definitions for ad nauseam that I've seen before include "Excessively, to a sickening extent" , "Much too much" , "to an excessive extent" , "Past the stage of enjoying" , "Repeating" .)