Model office worker keeping you waiting? (8)
I believe the answer is:
template
'model' is the definition.
(template is a kind of model)
'office worker keeping you waiting?' is the wordplay.
'office worker' becomes 'temp' (I've seen this before).
'keeping you waiting?' becomes 'late'.
'temp'+'late'='TEMPLATE'
(Other definitions for template that I've seen before include "Design model" , "original design" , "Shape serving as model" , "Model, example to follow" , "Model from which copies are made" .)