Bhal, a Néill,"Plancadh" Ó Dónaill lch 955 = "a beating / trouncing"
Three questions:
1. Whence came the intrusive "s" and "t" ?
2. More fundamentally why the Gen. Sg. Form "plancaidh" ?
3. Would you not expect the form "plancadh theach X" ?
Annraoi
N.B Tell your parents I send my regards.