Seminar arranged for servicemen (7)
I believe the answer is:
marines
'servicemen' is the definition.
(marine is a kind of serviceman)
'seminar arranged' is the wordplay.
'arranged' is an anagram indicator (letters rearranged).
'seminar' anagrammed gives 'MARINES'.
'for' is the link.
(Other definitions for marines that I've seen before include "Troops trained to serve on land or sea" , "Naval service" , "elite corps" , "Proverbial recipients of tall stories" , "forces" .)