Sphere concealed by floor boards (3)
I believe the answer is:
orb
'sphere' is the definition.
(I know that orb is a type of sphere)
'concealed by floor boards' is the wordplay.
'concealed by' indicates the answer is hidden within the clue.
'ORB' is hidden in the letters of 'floor boards'.
(Other definitions for orb that I've seen before include "ball with cross" , "Ceremonial globe carried by a monarch" , "Sovereign artefact" , "Heavenly body" , "Item of insignia" .)