1d) Former batsman in competition goes on to a century (7)
3d) Wood-supplier's left to fill big space for printer (3)
9a) The least revealing dress mother left (7)
Thanks
EM is a Printer's measure namely the width of a square or nearly square piece of type, used as a unit of measure for matter set in that size of type.
So it's EM + L (for left) = ELM (wood/tree)