sledge (n.1) Look up sledge at
"heavy hammer," Old English slecg "hammer, mallet," from Proto-Germanic *slagjo- (cognates: Old Norse sleggja, Middle Swedish sleggia "sledgehammer"), related to slege "beating, blow, stroke" and slean "to strike" (see slay (v.)). Sledgehammer is pleonastic.
sledge (n.2) Look up sledge at
"sleigh," 1610s, from dialectal Dutch sleedse, variant of slede (see sled (n.)); said by OED to be perhaps of Frisian origin.