Numerous staff getting on with uncertainty first (8)
I believe the answer is:
'numerous' is the definition.
(I've seen this before)
'staff getting on with uncertainty first' is the wordplay.
'staff' becomes 'man' (as in staffing or manning a particular place).
'getting on' becomes 'old' ('getting on a bit' means 'old').
'with' means one lot of letters go next to another.
'uncertainty first' becomes 'if' (I can't explain this - if you can you should give a lot more credence to this answer).
'old' after 'if' is 'ifold'.
Can you help me to learn more?
(Other definitions for manifold that I've seen before include "Diverse like engine part?" , "of numerous parts" , "maths set" , "Abundant" , "Many and various" .)