Ó Droighneáin, Gaelic-Irish surname.
Ó Droighneáin was a surname of at least two different septs, located in Counties Cork and Galway, but has been 'translated' as Thornton, an English surname.
The connection is: draighean, blackthorn; sceach, whitethorn; tor, a bush.
MacLysaght remarks that some Thorntons in Limerick were 16 cent planters".
[1] Ó Droighneáin remains in use as an Irish-language surname.