legalyoudaoicibaDictYouDict[legal 词源字典]
legal: [16] The Latin term for a ‘law’ was lex. From its stem form leg- come English legal, legislator [17] (which goes back to a Latin compound meaning literally ‘one who proposes a law’), and legitimate [15]. Loyal is a doublet of legal, acquired via Old French rather than directly from Latin. Another derivative of legwas the Latin verb lēgāre ‘depute, commission, bequeath’, which has given English colleague, college, delegate [14], legacy [14], and legation [15].
=> colleague, college, delegate, legacy, loyal[legal etymology, legal origin, 英语词源]
legal (adj.)youdaoicibaDictYouDict
mid-15c. "of or pertaining to the law," from Middle French légal or directly from Latin legalis "legal, pertaining to the law," from lex (genitive legis) "law," possibly related to legere "to gather," on notion of "a collection of rules" (see lecture (n.)).

Sense of "permitted by law" is from 1640s. Related: Legally. The Old French form was leial, loial (see leal, loyal). Legal tender is from 1740.