Senseless expedition beginning thus? (5)
I believe the answer is:
inane
'senseless' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for inane that I've seen before include "Vapid, fatuous" , "Lacking sense, silly" , "Fatuous, vacuous" , "Idiotic" , "Unintelligent" .)