▪ I. al- prefix1
The assimilated form of L. ad- to, before l. In OFr. reduced to a-, as in alier, for which however al- was often restored as an ‘etymological’ spelling in 14–15th c. in Fr. and Eng. In modern words adopted or formed from Latin the al- is always retained, as allegation, alliterate. Sometimes erroneously for a- in other words as a(l)lay.
▪ II. al- prefix2
The Arabic article the, retained as an essential part of the word in various words of Arabic origin, adopted in Eng. as alcohol, alcove, alcoran, algebra, alkali, almagest, almanac, etc.