Half-price tent is deployed, initially (2,3,5,5)
I believe the answer is:
in the first place
'initially' is the definition.
(I've seen this before)
'half-price tent is deployed' is the wordplay.
'deployed' indicates an anagram.
'half'+'price'+'tent'+'is'='halfpricetentis'
'halfpricetentis' is an anagram of 'IN THE FIRST PLACE'.
(Other definitions for in the first place that I've seen before include "Where the winner would be" , "Where Adam and Eve lived" , "Initially" , "originally" , "to begin with" .)