ap- (1) Look up ap- at Dictionary.com
form of Latin ad- before words beginning in -p-; see ad-.
ap- (2) Look up ap- at Dictionary.com
patronymic prefix in Welsh names, earlier map "son," cognate with Gaelic mac. Since 17c. merged into surnames (Ap Rhys = Price, Ap Evan = Bevan, etc.).
It is said that a Welshman who evidently was not willing to be surpassed in length of pedigree, when making out his genealogical tree, wrote near the middle of his long array of 'aps' -- "about this time Adam was born." ["Origin and Significance of our Names," "The Chautauquan," Oct. 1887-July 1888]