In a manner of speaking, I had one on order (5)
I believe the answer is:
idiom
'in a manner of speaking' is the definition.
(I've seen this before)
'i had one on order' is the wordplay.
'i had' becomes 'id' (I'd).
'one' becomes 'i' (Roman numeral).
'on' is a charade indicator (letters next to each other).
'order' becomes 'om' (order of merit).
'id'+'i'+'om'='IDIOM'
(Other definitions for idiom that I've seen before include "Group of words in which the meaning may not be obvious" , "Artistic style" , "Way of speaking" , "Form or variety of language" , "Peculiarity of phrase in a language" .)