||To beat severly (usually with some implement).
||I leddered him.
I gave him a severe beating.
||Possibky Irish 'Leadar√°il' - act of lashing. (Dinneen)
or possibly a corruption of 'Leather' - a leather strap used to punish pupils at school.
But note 'Leather' - to beat. This is not derived as might be supposed from the English word leather (tanned skin), but from the Irish in which it is of very old standing: 'Letrad' (modern 'Leadradh') - cutting, hacking, lacerating, also a champion fighter, a warrior, a leatherer. (Corm. Gloss, 9th century). (Joyce)
'Ledder' probably a corruption of a heavy blow. (Wright)
Note 'Leadradh' - striking, tearing, cuttin, dissecting, whipping, destroying. (Dinneen)
and 'Leadradh' - a thrashing and "Leadrah a fh√°il - to get a leathering". (√ď Domhnaill)
and 'Leather' - to beat, thrash. (Partridge)