Most determined to make uniform, then relax (7)
I believe the answer is:
dourest
'most determined' is the definition.
'make uniform then relax' is the wordplay.
'make' becomes 'do' (doing is a kind of making).
'uniform' becomes 'u' (phonetic alphabet: alpha, bravo, charlie etc.).
'then' means one lot of letters go next to another.
'relax' becomes 'rest' (I've seen this before).
'do'+'u'+'rest'='DOUREST'
'to' acts as a link.
(Other definitions for dourest that I've seen before include "Grimmest" , "Most forbidding" .)