The surname originated as a patronym, however it no longer refers to the actual name of the bearer's father.

A cognate of Mac Amhalghaidh is the Scottish Gaelic MacAmhalghaidh; the feminine form of which is NicAmhalghaidh.

[2] The surname originated as a patronym, however it no longer refers to the actual name of the bearer's father.

The personal name Amhalghaidh, also spelt Amhalghadh, is an old Gaelic name, and is of uncertain origin and meaning.

This feminine name is composed of the prefix Nic-, which is an abbreviated form of the Scottish Gaelic nighean mhic[5] or nì mhic,[6] which translates into English as "daughter of the son"; thus NicAmhalghaidh translates as "daughter of MacAmhalghaidh".

Anglicisations in use today include Cauley,[8] Cawley,[1] Macally,[10] MacAlley,[10] MacAulay,[10] MacAuley,[10] MacAuliffe,[10] Maccally,[10] MacCauley,[1] MacCawley,[8] and MacCowley,[1] MacGawley, and Magawley.

The most notable of these was a particular family that was historically seated in what is today County Westmeath, Republic of Ireland.

A pedigree of the family is recorded stretching back to Niall of the Nine Hostages, a semi-legendary High King of Ireland.

[2][4] The early ancestry of the MacAulays is uncertain, although their surname may ultimately be linked to members of the original family of the Earls of Lennox, who bore the name Amhalghaidh / Amhalghadh.