13th cent. Borrowed from Old Occitan balar 'id.' However the appurtenance of -i- in the Spanish is inexplicable. Of note is Pyrenees dialect variant and Aragonese dialect variant bailar "to sway," from Latin baiulare "to carry a burden." Because a borrowing from Old Occitan is more likely than from a dialect oddball in Aragonese, and because the semantics in Occitan are identical to Spanish, it is easier to accept the theory that bailar is a loan from Old Occitan balar with an unexplained diphthongization. The native Old Spanish word for dancing was sotar (see jota (2)). Balar is from Latin ballare "to throw." Borrowed from Ancient Greek βάλλειν (bállein) 'id.' (see diablo).
Pyrenees balar "to sway," Asturian balar 'id.'