ladder (n.) Look up ladder at Dictionary.com
Old English hlæder "ladder, steps," from Proto-Germanic *khlaidri (cognates: Old Frisian hledere, Middle Dutch ledere, Old High German leitara, German Leiter), from PIE root *klei- "to lean" (cognates: Greek klimax "ladder;" see lean (v.)). In late Old English, rungs were læddrestæfæ and the side pieces were ledder steles. The belief that walking under one brings bad luck is attested from 1787, but its origin likely is more pragmatic than symbolic. Ladder-back (adj.) as a type of chair is from 1898.