How can I copy the definition of a field from one table to another at design-time?
I would like to copy those field definitions to another table, without needing to re-write the whole definitions.

How about this?
create table t2 as 
select * 
from t1 
where 1 = 2 ; 

OK, it doesn't copy indexes and such like, but it gets you the basic structure, as requested.

I'm working with the Data Dictionary, who seems not to cover this feature.

Given that the job of a Data Dictionary is to manage the structures of other tables, I'd say that's a pretty big hole in its functionality!