Regularly observed inbound sight maybe? Balderdash (8)
I believe the answer is:
nonsense
'balderdash' is the definition.
(I've seen this before)
'regularly observed inbound sight maybe?' is the wordplay.
'regularly observed' indicates alternate letters (letters selected at regular intervals).
'sight maybe?' becomes 'sense' (I can't justify this - if you can you should believe this answer much more).
The alternate letters of 'inbound' are 'non'.
'non'+'sense'='NONSENSE'
Can you help me to learn more?
(Other definitions for nonsense that I've seen before include "Bull" , "Rubbish, drivel" , "Baloney" , "Bunk" , "'Foolishness, silliness (8)'" .)