Whistle-blower interrupts work in clover (7)
I believe the answer is:
trefoil
'clover' is the definition.
(I know that clover can be written as trefoil)
'whistle-blower interrupts work' is the wordplay.
'whistle blower' becomes 'ref' (a referee blows a whistle).
'interrupts' means one lot of letters goes inside another.
'work' becomes 'toil' (toiling is a kind of working).
'ref' going into 'toil' is 'TREFOIL'.
'in' is the link.
(Other definitions for trefoil that I've seen before include "Small clover-like plant" , "Three-lobed leaf" , "clover, possibly" , "Clover leaf" , "Loftier (anag) -- clover-like plant" .)