Hi
I would like to know the opposite of the word punctual. Please see below:
1- Although his brother is regular and punctual, he is very irregular and [color=red]unpunctual.
How does it sound to you?
Tom
I know unprecise
But am not sure with the example.
There is no opposite word.
It depends on the context: one might say “not punctual”
“not very punctual” or “often late”.
Hi Tom
The usual opposite for punctual would be late.
I feel a little uncomfortable with “regular and punctual”, so that makes saying the opposite even more difficult. 
Exactly what tendency (of his personality/character) did you want to call “regular”?
Here is a suggestion:
Although his brother is very dependable and always punctual, he is quite undependable and frequently late.
Note to Tamara:
The standard word would be imprecise.
Amy
Yes, Amy, you’re right. I often mix them up, thank you for your correction.
I know imprecise, it is widely used as a technical/Math term used in calculation.
But …‘non-standard’ unprecise is also in use… in fact…
Take a look, for example, at the heading: webrankinfo.com/english/seo- … ic-301.htm
But …‘non-standard’ unprecise is also in use… in fact…
Take a look, for example, at the heading: webrankinfo.com/english/seo- … ic-301.htm
Hi Tamara,
I think Yankee is correct. The term “unprecise” is not good English. However wrote the example you refer to is mistaken.
Art
Hi dOlier,
Thank you very much for your thought.
I’d like to add something that has nothing to do with your initial question, Tom.
The use of the pronoun ‘he’ in the second clause might be a little confusing, I think. In fact, when first reading the sentence, I thought the second clause was still referring to ‘his brother’. I’d prefer to use a noun instead:
Although his brother is regular and punctual, Tom (my new student, your friend, etc.) is often late.
As an afterthought, I’d take out ‘regular’. Have you seen this definition for the word 
?: