leprechaun (n.)

c. 1600, from Irish lupracan, metathesis of Old Irish luchorpan literally "a very small body," from lu "little, small" (from PIE root *legwh- "not heavy, having little weight") + corpan, diminutive of corp "body," from Latin corpus "body" (from PIE root *kwrep- "body, form, appearance").

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."