Time keeper
I think it could be either:
'time keeper' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for metronome that I've seen before include "Device for keeping time" , "Device to indicate tempo" , "Ticker setting tempo of music" , "Musician's time device" , "Musician's timekeeper" .)
(Other definitions for newsstand that I've seen before include "Where papers are sold" , "On which papers sit" , "Where to buy papers" , "Where to pick up the Guardian?" , "Wants dens (anag.)" .)