[semeai]

Both 1♦ and 2NT seem fine. Especially during an indy opposite a professed beginner I might choose 2NT.

[losercover]

I thought bidding NT with a singleton was ok as a very rare event. That it couldn't be done with any frequency. Am I wrong? Is there a difference regarding shape between 1NT and 2NT? We play a very strong 1NT (19-21) and try to limit one bids to a max of 18 points. With a 3 suited hand and 19+ HCP we open 2C and partner responds control steps. Opener rebids NT at the lowest level (which is alerted)and responder and opener bid their suits up the line until a fit is found. Surprisingly, we have good results doing this. If I could get away with an out of shape 1NT, I might consider doing using it with all responses as standard to a NT opening.

[JLOGIC]

I don't think exactly 4441 with a stiff K in a minor is all that frequent

[Foxx]

In my opinion, opening 1NT or 2NT with 4-4-4-1 distribution is all right if the singleton is specifically the K. Opening 1NT or 2NT with a singleton A or Q is more iffy, but still tolerable.

A couple of years ago, I was in a club game and opened 1NT with 16 HCP and a singleton ♥K. Partner transferred to hearts and drove me to 5♥ with a good hand that included ♥AJ10xxx. I was a big underdog to make it, but we got bailed out when the ♥Q fell doubleton.

My judgment call caused quite a row, which involved my partner, our opponents, and the club director. I argued that opening 1NT with a singleton should be OK if it's the king, while the director told me that if I made a regular practice out of notrump openings with singletons, my partner would have to alert it. Hmmm.

The justification for opening in notrump with a singleton K is that it's most likely to combine with partner's holding to stop the suit at notrump. With a singleton Q, this is somewhat less likely, while a singleton A means no losers in the suit and therefore makes the hand better for suit play if you have a fit.