Plan a series of lectures (6)
I believe the answer is:
course
This clue is a triple definition!
'plan' is the first definition.
(thesaurus)
'a series' is the second definition.
(course is a kind of series)
'of' is a link.
'lectures' is the third definition.
(a course can be a series of lectures)
(Other definitions for course that I've seen before include "programme for students" , "Woman's dress" , "Path of a river or a set of lessons" , "Curriculum" , "way" .)