Fixed frequency in distributed datasets (9)
I believe the answer is:
steadfast
'fixed' is the definition.
(I've seen this before)
'frequency in distributed datasets' is the wordplay.
'frequency' becomes 'F' (abbreviation e.g. FM radio).
'in' means one lot of letters goes inside another.
'distributed' indicates anagramming the letters.
'datasets' with letters rearranged gives 'steadast'.
'f' put inside 'steadast' is 'STEADFAST'.
(Other definitions for steadfast that I've seen before include "Dedicated" , "Fixed, unyielding" , "Resolute, unwavering" , "Resolutely firm" , "Firm and unwavering" .)