Inadequate display after online address is replaced by computer department (5)
I believe the answer is:
unfit
'inadequate' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for unfit that I've seen before include "Ill - out of shape" , "Not prepared" , "Not in good physical condition, or not suitable" , "Not in good physical shape (5)" , "In bad physical condition" .)