Green’s Dictionary of Slang

adad! excl.

God!

c.1642		T. Killigrew Parson’s Wedding (1664) II v: wild: I must see the Wench. capt.: You cannot, a dad, a dad you cannot.
1681		Otway Soldier’s Fortune I i: I had rather all the relations I have were dead; a-dad, I had.
1688		T. Shadwell Squire of Alsatia I i: An you mutter one word more, adad I’ll mince you.
1706		R. Estcourt Fair Example III iii: Adad, I think this Wine makes my Head a little giddy.
1728		Vanbrugh & Cibber Provoked Husband V ii: Adad! I have a Thought in my Head, Madam.
1753		Richardson Sir Charles Grandison (1812) VI 541: ‘Adad, adad,’ said he, ‘I do not know what to make of myself.’.
1763		I. Bickerstaff Love in Village 37: Why, you look as fresh and bloomy to-day. Adad, you little slut, I believe you are painted.
a.1770		T. Chatterton ‘Memoirs of a Sad Dog’ Misc. (1778) 197: Adad, thou art in the right.