Cross about dates with duke — not thinking clearly (7)
I believe the answer is:
muddled
'not thinking clearly' is the definition.
(muddled can mean confused or unclear)
'cross about dates with duke' is the wordplay.
'cross' becomes 'mule' (a mule is a cross of a donkey and a horse).
'about' indicates putting letters inside.
'dates' becomes 'dd' (an abbreviation for date written twice).
'with' says to put letters next to each other.
'duke' becomes 'd' (abbreviation).
'mule' placed around 'dd' is 'muddle'.
'muddle'+'d'='MUDDLED'
(Other definitions for muddled that I've seen before include "Disordered, confused" , "Confused, all mixed up" .)