Symbol of sturdiness (3)
I believe the answer is:
oak
'symbol of sturdiness' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for oak that I've seen before include "Grown acorn" , "The King of the Forest" , "Tree of the genus Quercus" , "From little acorns does it grow" , "Building timber" .)