Two merged words: the vehicle from Proto-Germanic *slidō (to slide), the hammer from *slagjō (to strike).
A vehicle on runners for transporting loads over snow or ice; also, a heavy hammer used by blacksmiths.
The vehicle sense from Middle Dutch 'sleedse,' from 'slee' (sled), from Proto-Germanic *slidō (a sliding thing). The hammer sense is separate, from Old English 'slecg' (heavy hammer), from Proto-Germanic *slagjō (striker), from 'slahan' (to strike). Key roots: *slidō (Proto-Germanic: "to slide").