Option of engineers joining series of lectures (8)
I believe the answer is:
recourse
'option' is the definition.
(recourse can mean an option or possibility)
'engineers joining series of lectures' is the wordplay.
'engineers' becomes 're' (Royal Engineers).
'joining' says to put letters next to each other.
'series of lectures' becomes 'course' (I've seen this before).
're'+'course'='RECOURSE'
'of' acts as a link.
(Other definitions for recourse that I've seen before include "One resorted to" , "Refuge, resort" , "Help; option" , "Legal right to demand payment" , "Expedient" .)