Figure needing support to involve personnel department (5)
I believe the answer is:
three
'figure' is the definition.
(three is a number or figure)
'support to involve personnel department' is the wordplay.
'support' becomes 'tee' (tee is a kind of support).
'to involve' means one lot of letters goes inside another.
'personnel department' becomes 'HR' (Human Resources).
'tee' enclosing 'hr' is 'THREE'.
'needing' is the link.
(Other definitions for three that I've seen before include "Figure" , "Trinity, triad" , "Number of times N appears in this completed grid" , "Sixth root of seven hundred and twenty nine" , "trilogy" .)