A measure of work in a lot of organs (3-5)
I believe the answer is:
man-years
'a measure of work' is the definition.
(a man-year is a year's worth of work)
'a lot of organs' is the wordplay.
'a lot of' becomes 'many' (many means a lot).
'organs' becomes 'ears' (ear is a kind of organ).
'many'+'ears'='MAN-YEARS'
'in' acts as a link.
(Other definitions for man-years that I've seen before include "quantity of work" , "Units of work effort" .)