Thick and Thin by Foxymoron

The phrase (through) "thick and thin" comes from Old English, and was originally "through thicket and thin wood", meaning to cope with difficulties and to enjoy easier periods. The earliest known reference is from Chaucer's The Reeve's Tale

And whan the hors was laus, he gynneth gon

Toward the fen, ther wilde mares renne,

And forth with “wehee,” thurgh thikke and thurgh thenne.

In some usage, thick and thin are antonyms. But not in bridge. Thick in bridge is not a compliment, and indicates that you have done something stupid. As in Henry IV, Part 2:

Hang him baboon, his wit’s as thicke as Tewksbury mustard.

I was certainly thick, and felt like a baboon, in last week's duplicate when I only made seven tricks on the following hand in 1NT as North:

East led a normal spade, and West played the king, and I played the jack, the card I was planning to play on the next round ... Not really a mispull, just thick. Now the defence cashed five rounds of spades, and could have beaten me two tricks if they had switched to a club, but +90 was hardly any match points anyway.

Thin in bridge is not the opposite of thick, but refers to a contract, usually slam or game, that has a very low chance of success. Such was the case with the following hand.

We bid 1H-(2C)-3C*-(4C)-6H-All Pass. Three Clubs was a good raise. My partner was a bit unlucky that my ace of clubs was of no value and that there was a trump loser. But was there? West led the ace of diamonds, and another diamond. South won and now effectively gave up by cashing the ace of hearts. However, as the chess grandmaster Savielly Tartakower said, "No game is won by resigning".  A singleton king of trumps is about as much use as a chocolate teapot, an expression which appears to be mid-20th century.

Declarer should have crossed to dummy with a spade, and run the queen of hearts. East can cover, but you cross again in spades and run the eight of hearts to bring home your thin slam. This was the only chance and mirabile dictu it would have worked.

How thin is the slam? Quite easy to calculate as the chance of East having three hearts and West one is about 25%, and you need a singleton jack with West, which occurs one quarter of that time. So, about 6.25%. How thick was my partner? I will leave you to judge!