Elaborate (9)
(Other definitions for expatiate that I've seen before include "Go into detail" , "Speak or write at length about subject" , "Go on at length" , "Elaborate" , "Make detailed speech" .)
'elaborate' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for complicated that I've seen before include "Tricky" , "Not simple" , "confused" , "Intricate, difficult" , "consisting of many interconnecting parts" .)