To understand a language’s idioms, is to be fluent in the language.  Maybe this isn’t entirely true, but it’s close.

When I lived in England, I remember being stumped by the phrase, “it’s like money for old rope.”  I didn’t know if that meant: 1) someone had given me money for old rope–in which case, that was a good thing; or 2) I was paying money for old rope–meaning I was getting ripped off.  As it turns out, the saying “originates from the days of public hangings. It was a perquisite of the hangman to keep the rope used to hang his ‘customer’. The rope, however, was popular with the macabre crowds, so the hangman used to cut the rope up and sell it.”  That still doesn’t tell me whether paying for it a good or bad thing 🙂  This site tells me “if a job is money for old rope, it is an easy way of earning money.”

Welsh, then, has idioms too, many of which are undoubtedly impenetrable to an American as the English ones.  Many are the same or similar, which isn’t terribly surprising given that Wales was conquered by England 700 years ago.  Here are some that are similar to English and yet different:

Take care lest you buy a cat in a sack / = pig in a poke in English. (Cymerwch ofal rhag ofn i chi brynu cath mewn cwd.)

It’s raining old ladies and sticks / knives and forks / = cats and dogs in English. (Mae hi’n bwrw hen wragedd a ffyn / cyllyll a ffyrc.)

They were tight like herrings in the salt / = sardines in a tin. (Roedden nhw’n dynn fel penwaig yn yr halen.)

My son was the candle of my eye / = apple of my eye. (Cannwyll fy llygad oedd fy mab.

I opened the door with my heart in my throat / = heart in my mouth. (Agorais y drws a’m calon yn fy ngwddf.)

The old woman always talked fifteen in the dozen / = nineteen to the dozen.  (Siaradai’r hen wraig pymtheg yn y dwsin bob amser.) 

The dog was as dead as a coffin nail / = as dead as a doornail. (Roedd y ci cyn farwed â hoelen arch.)

http://www.madog.org/dysgwyr/gramadeg/gramadeg3.html

And then others that are nothing like English:

He rushed into the house with his breath in his fist / = in a great hurry. (Rhuthrodd ef i’r ty^ ‚’i wynt yn ei ddwrn.)

I’m ready to put the fiddle in the roof / = to give up. (Rwy’n barod i roi’r ffidil yn y tô.)

My grandfather’s in the fords of the river / = on his death bed. (Mae fy nhad-cu yn rhydiau’r afon.)

I’ll give my head for breaking / = I’m absolutely certain / they’ll get married. (Mi rown fy mhen i’w dorri y byddan nhw’n priodi.)

She talks like a pepper mill / = talks non-stop. (Mae hi’n siarad fel melin bupur.)

I’m looking forward to lighting a fire on an old hearth / = renewing an old love. (Rwy’n edrych ymlaen at gynnu tân ar hen aelwyd.)

She is the eye of her place / = totally correct in her opinion. (Mae hi yn llygad ei lle yn ei barn)

These idioms appear in Llyfr o Idiomau Cymraeg by R. E. Jones, published by Gwasg John Penry. The same author has also produced a second volume, Ail Lyfr o Idiomau Cymraeg.

And there’s more:  http://www.britannia.com/fame/fame.html

A horse in front = in the spotlight (ceffyl blaen)

Comes the sun to the hill = things will get better (daw haul ar fryn)

Like killing snakes = very busy (fell lladd nadroedd)

No Welsh between them = they’re not speaking to each other (Dim Cymraeg rhyngddynt)

The wheel has turned  = times have changed. (mae’r olwyn wedi troi)