Colonel losing millions: not what one expected? (4)
I believe the answer is:
blip
'not what one expected?' is the definition.
(a blip is an unexpected development)
'colonel losing millions' is the wordplay.
'colonel' becomes 'blimp' (cartoon character Colonel Blimp).
'losing' indicates named letters should be taken away.
'millions' becomes 'm' (abbreviation).
'blimp' with 'm' taken away is 'BLIP'.
(Other definitions for blip that I've seen before include "Glitch" , "Unforeseen irregularity" , "Temporary irregularity" , "Signal on a radar screen" , "Hiccup" .)