Old land use system's one required over in Florida (6)
I believe the answer is:
feudal
'old land use system's' is the definition.
'feudal' can be an answer for 'system's' (feudal system is a kind of system). I am unsure of the 'old land use' bit.
'one required over in florida' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'required' becomes 'due' (due can mean required or expected).
'over' says the letters should be written in reverse.
'in' means one lot of letters goes inside another.
'florida' becomes 'fl' (abbreviation for Florida).
'a'+'due'='adue'
'adue' back-to-front is 'euda'.
'euda' inserted within 'fl' is 'FEUDAL'.
Can you help me to learn more?
(Other definitions for feudal that I've seen before include "Relating to vassalage" , "Pertaining to fiefs" , "Resembling or relating to a medieval social system" , "Of system of land-holding in Middle Ages" , "Kind of system of holding land in Middle Ages" .)