dweud y drefn

Literally “to say the (proper) order, to say the rule”.

dweud y drefn (first-person singular present dywedaf y drefnaf)

1. (intransitive) to lay down the law

   Synonym: rhoi'r ddeddf i lawr

2. (with wrth) to tell off, to scold

   Synonyms: ceryddu, dwrdio, dannod

• R. J. Thomas, G. A. Bevan, P. J. Donovan, A. Hawke et al., editors (1950–present), “dweud y drefn”, in Geiriadur Prifysgol Cymru Online (in Welsh), University of Wales Centre for Advanced Welsh & Celtic Studies