sledge (n.1) Look up sledge at Dictionary.com
"heavy hammer," Old English slecg, from Proto-Germanic *slagj- (cf. Old Norse sleggja, Middle Swedish sleggia "sledgehammer"), related to slean "to strike" (see slay). Sledgehammer thus is pleonastic.
sledge (n.2) Look up sledge at Dictionary.com
"sleigh," 1610s, from dialectal Dutch sleedse, variant of slede (see sled (n.)); said to be of Frisian origin.