perhaps Gaelic?

[rcdawson]

I am of Scottish ancestry. My Grandfather said he had a good "COD" (or CAUD) on someone, meaning a good joke on him/her. Can you tell me the derivation?
Ron Dawson

[BobK]

I am of Scottish ancestry. My Grandfather said he had a good "COD" (or CAUD) on someone, meaning a good joke on him/her. Can you tell me the derivation?
Ron Dawson

The OED (subscription only, so no link I'm afraid) says

...A joke; a hoax, leg-pull; a parody, a ‘take-off’. (See also E.D.D. n.5) Also attrib. or quasi-adj., parodying, burlesque; ‘mock’.
1905 Sketch LI. 472/2 Says he: ‘Is that an absolute bargain{em}no cod?’ Says she: ‘I don't know what the fish has to do with it, but I am perfectly sincere....

And there's nothing under 'caud'. Another meaning of 'cod' (that one was n5, this is n2) is given as Scottish:

1. A pillow; a cushion. Sc. and north. dial.
a1400-50 Alexander 4916 With curtyns all of clene sylke & coddis of {th}e same...

b

[rcdawson]

Great! Thank you.
Another was that someone disliked was called "an old plut-ther". A useless person or thing was called a "fooot-ther". Both were sort of all-encompassing terms. Might these also have been from the Gaelic? Pardon my phonetic spellings but I never saw the words in print.
Ron Dawon

[Anglika]

Probably Scots rather than Gaelic: The Online Scots Dictionary - Home Page

[mmasny]

From Webster's:

cod vb [origin unknown] dial : TEASE, HOAX, BANTER, KID
cod N dial : HOAX

They are supposed to point it out that a word is Scots, so, as they say it's dialectal, it is or was probably used somewhere outside Scotland too. As you can see they don't know where it comes from.
There's no caud there. They don't have it in http://www.dsl.ac.uk/dsl/ either.