Douglas Harper's Etymology Dictionary
patronymic prefix in Welsh names, earlier map "son," cognate with Gaelic mac. Since 17c. merged into surnames (Ap Rhys = Price, Ap Evan = Bevan, etc.).\n\nIt 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]
form of Latin ad- before words beginning in -p-; see ad-.
Usage examples of "ap-".
Just another soap-bubble illusion burst by the cold reality of this awful place.
The slap-slap of their rag-and-hide-wrapped feet on the metal stairs rose to Smith.