Crack up and pass, by mistake (8)
I believe the answer is:
collapse
'crack up' is the definition.
(synonyms)
'pass by mistake' is the wordplay.
'pass by' becomes 'col' (col is a kind of pass. I am not sure about the 'by' bit.).
'mistake' becomes 'lapse' (lapse is a kind of mistake).
'col'+'lapse'='COLLAPSE'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for collapse that I've seen before include "Fall down as from weakness" , "Fall down or lose strength suddenly" , "Fall down unconscious" , "Sudden breakdown" , "Go to ruin" .)