leprechaun (n.) Look up leprechaun at Dictionary.com
c. 1600, from Irish lupracan, metathesis of Old Irish luchorpan literally "a very small body," from lu "little" (from PIE *legwh- "having little weight;" see light (adj.)) + corpan, diminutive of corp "body," from Latin corpus "body" (see corporeal).

Commonly spelled lubrican in 17c. English; "Century Dictionary" (1902) has it under leprechawn. Variant leithbragan probably is Irish folk etymology, from leith "half" + brog "brogue," because the spirit was "supposed to be always employed in making or mending a single shoe."