Pounds a bit short, saving one in case for a significant event (9)
I believe the answer is:
milestone
'for a significant event' is the definition.
(I've seen this in another clue)
'pounds a bit short saving one in case' is the wordplay.
'pounds' becomes 'money' (pounds sterling).
'a bit short' means to remove the last letter.
'saving' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'in case' becomes 'lest' (I've seen this in another clue).
'money' with its final letter taken away is 'mone'.
'i'+'lest'='ilest'
'mone' going around 'ilest' is 'MILESTONE'.
(Other definitions for milestone that I've seen before include "Wayside indicator" , "Significant event or stage - a measure" , "Important stage (reached)" , "Significant developmental stage" , "Pillar" .)