"Byddwch yn dawel nawr!"
Translation:Be quiet now!
"Dawel" would be related to "Mo^r Tawel"? ("Pacific" means "peaceful", and a pacifist is a peace-maker.)
Is there a more emphatic way of saying this in Welsh? i.e. "Shut up!" vs. "Be quiet!"?
You can use 'tawel' itself
Tawelwch! = Quieten!, Silence!
Byddwch yn dawel! is also an emphatic sentence, it's a command.
All the b- forms of the verb bod are cognate with the b- forms of the English verb to be, and also with the Latin verbs fio ("I become; I happen", as in fiat lux, "let there be light", and also origin of Romanian a fi, "to be") and the f- forms of vado ("I go"), like fui ("I went"), and also of futurus ("future"). The same root is also present in the Latin suffix -bo ("future suffix", like in amabo, "I will love") and -bam ("imperfective indicative suffix", like in amabam, "I was loving"). The former suffix was lost in all the Romance languages (in this example, Spanish amaré, which uses an unrelated suffix), while the latter was successfully transmitted (Spanish amaba).