Formidable female has uniform in wash (9)
I believe the answer is:
herculean
'formidable' is the definition.
(thesaurus)
'female has uniform in wash' is the wordplay.
'female has' becomes 'her' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' means one lot of letters goes inside another.
'wash' becomes 'clean' (I've seen this before).
'u' put within 'clean' is 'culean'.
'her'+'culean'='HERCULEAN'
Can you help me to learn more?
(Other definitions for herculean that I've seen before include "Old Labour" , "Enormously demanding (task)" , "Monumental (task)" , "Requiring very great effort" , "Showing great strength" .)