More than one is involved in project work (3)
I believe the answer is:
two
'more than one' is the definition.
(I've seen this in another clue)
'involved in project work' is the wordplay.
'involved in' indicates a hidden word.
'TWO' can be found hidden inside 'project work'.
'is' acts as a link.
(Other definitions for two that I've seen before include "Even number" , "2" , "Minimal number of partners" , "eg Twins" , "Number of faces of the god Janus" .)