Just so I'm prepared, what is Welsh for "We must hide the body"?
"Heddlu" sounds like "Heavy" to me, an informal way of say "Police".
I wonder if there's a relationship between the two.
Edit: I'm thinking that "Heavy", in this sense, could be seen as an anglefication of "Heddlu".
Heddlu comes from hedd = peace and llu = a host/force, so no relation to heavy - unless it helps you remember the word!