baldyoudaoicibaDictYouDict[bald 词源字典]
bald: [14] In Middle English times, bald was ballede, which suggests that it may have been a compound formed in Old English with the suffix -ede ‘characterized by, having’. It has been conjectured that the first element in the compound was Old English *ball-, meaning ‘white patch’ or ‘blaze’ on an animal’s head; this may be supported by isolated examples of the use of the adjective to mean (of a horse) ‘whitefaced’ from the 16th to the 18th centuries, and by the obsolete dialectal ball meaning both ‘white patch on the head’ and ‘white-faced horse’.

This would have produced the Old English adjective *bællede or *beallede, which, from ‘having a white blaze’, progressed naturally in meaning to ‘hairless’. The compounds piebald [16] and skewbald [17] are both based on bald: piebald means ‘having black and white patches like a magpie’, while skewbald may be based on Middle English skew ‘(cloudy) skies’ or on Old French escu ‘shield’.
=> piebald, skewbald[bald etymology, bald origin, 英语词源]
bald (adj.)youdaoicibaDictYouDict
c. 1300, ballede, probably, with Middle English -ede adjectival suffix + Celtic bal "white patch, blaze" especially on the head of a horse or other animal (from PIE root *bhel- (1) "to shine, flash, gleam;" see bleach (v.)). Compare, from the same root, Sanskrit bhalam "brightness, forehead," Greek phalos "white," Latin fulcia "coot" (so called for the white patch on its head), Albanian bale "forehead." But connection with ball (n.1), on notion of "smooth, round" also has been suggested. Bald eagle first attested 1680s; so called for its white head.