English terms which no longer mean what they (literally) say.
The classic examples are probably "RAM" and "ROM", derived respectively from "random-access memory" and "read-only memory" and literally rendered into official Irish respectively as "cuimhne randamrochtana" (FR 301) and "cuimhne inléite amháin" (FR 302), earlier "cuimhne léimh amháin" (TR 162).
In fact, English-speaking computer users don't give a thought to the origins of the terms RAM and ROM. They know that RAM and ROM are two kinds of computer memory which reside on memory chips, and the difference between them is that the content of ROM is fixed whereas the content of RAM can be changed. This is what the terms mean, and that meaning has to be learned, without much assistance from the form of the terms themselves. But at least those terms are concise, and because of their etymological opaqueness they do not mislead.
If people tried to work out the meaning of RAM and ROM from the expressions "random-access memory" and "read-only memory", they would get very confused. Computer memory can reside on chips, on disks of various kinds, on tapes. All of these, except tape, are random-access. A hard disk, a floppy disk, a zip disk, a compact disk, and even ROM are all forms of random-access memory, but none of these is RAM. And a floppy disk, a zip disk, a backup tape — any of these with its write-protect mechanism activated is a form of read-only memory. So is a non-rewritable compact disk. Of course, none of them is ROM.
But the Irish user has only "cuimhne randam-rochtana" and "cuimhne inléite amháin" to help him! These root-transations capture all that is bad about the English terms, and lose the one thing that is good about them — their snappiness.
We must try again. Both RAM and ROM are forms of memory which reside on chips. That gives us "slis-chuimhne", which immediately makes it clear that we are not talking about memory on disks or tapes. We could distinguish between them by calling ROM "seasmhach" (immutable) and RAM "neamhsheasmhach" (mutable). Or some other pair of adjectives like "buan" and "luaineach". (French uses "memoire morte" vs "memoire vive".)
So, "slischuimhne sheasmhach" and "slischuimhe neamhsheasmhach". Not snappy, but certainly more easily pronouncable than the official terms. And most importantly, structurally conveying the correct meaning, not an incorrect meaning as the official terms do by following the literal derivations of the English.
For another case where literal translation of the English terms misleads, see the note on "virtual reality". Even if not misleading, literal translation of English may result in an unwieldy term when a more manageable and more systematic alternative is available, see the note on "fixed and variable". Unconsidered adherence to translation formulae such as "program" = "clár" and "key" = "eochair" and "save" = "sábháil" is another source of trouble, see the notes on "program" and "key" and "save".