Item posted conceals speed (5)
I believe the answer is:
tempo
'speed' is the definition.
(I've seen this before)
'item posted conceals' is the wordplay.
'conceals' indicates a hidden word.
'TEMPO' can be found hidden inside 'item posted'.
(Other definitions for tempo that I've seen before include "Rhythm or speed as in music" , "Speed of a musical piece" , "What a metronome provides" , "Pace - pacing" , "Rate and rhythm in music" .)