ladder (n.)

Old English hlæder "ladder, steps," from Proto-Germanic *hlaidri (source also of Old Frisian hledere, Middle Dutch ledere, Old High German leitara, German Leiter), from suffixed form of PIE root *klei- "to lean" (source also of Greek klimax "ladder"). In late Old English, rungs were læddrestæfæ and the side pieces were ledder steles. The belief that bad things happen to people who walk under ladders is attested from 1787, but its origin likely is more scientific than superstitious.

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Definitions of ladder from WordNet
ladder (n.)
steps consisting of two parallel members connected by rungs; for climbing up or down;
ladder (n.)
ascending stages by which somebody or something can progress;
he climbed the career ladder
ladder (n.)
a row of unravelled stitches;
Synonyms: run / ravel
ladder (v.)
come unraveled or undone as if by snagging;
Synonyms: run