Plan falling short, keeping fifty out of work (4)
I believe the answer is:
idle
'out of work' is the definition.
(I've seen this in another clue)
'plan falling short keeping fifty' is the wordplay.
'plan falling short' becomes 'ide' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'keeping' means one lot of letters goes inside another (some letters kept inside).
'fifty' becomes 'l' (Roman numeral).
'ide' going around 'l' is 'IDLE'.
Can you help me to learn more?
(Other definitions for idle that I've seen before include "staying in bed all day?" , "Indolent" , "Ineffectual" , "Frivolous" , "Not occupied" .)