Plant finally sent soldiers sword (7)
I believe the answer is:
trefoil
'plant' is the definition.
(trefoil is a kind of plant)
'finally sent soldiers sword' is the wordplay.
'finally' suggests the final letters.
'soldiers' becomes 're' (Royal Engineers).
'sword' becomes 'foil' (foil is a kind of sword).
The last letter of 'sent' is 't'.
't'+'re'+'foil'='TREFOIL'
(Other definitions for trefoil that I've seen before include "Three-leaf clover" , "Small plant with yellow flowers and three leaves - to rifle (anag)" , "Plant with three leaves, like shamrock or clover" , "Loftier (anag) -- clover-like plant" , "Plant with clover-like leaves" .)