Mistake by colonel resulting in breakdown (8)
I believe the answer is:
collapse
'breakdown' is the definition.
(synonyms)
'mistake by colonel' is the wordplay.
'mistake' becomes 'lapse' (lapse is a kind of mistake).
'by' is a charade indicator (letters next to each other).
'colonel' becomes 'col'.
'lapse' put after 'col' is 'COLLAPSE'.
'resulting in' acts as a link.
(Other definitions for collapse that I've seen before include "Go to ruin" , "Founder" , "fold" , "Suddenly fall down or give way" , "Sudden fall" .)