Etymological Notes
Knowledge of the way words are constructed, the ability to comprehend the exact meaning of words and the ability to form new words are skills that I believe good writers should be familiar with. This is the object of the field of etymology.
bi-: Latin: twice, two
Hence the ambiguity over words such as biweekly, which could mean twice a week OR once every two weeks. There is no such confusion over biennial, however, which always means once every two years.
dia-, di-: Greek: through, between, across, by, of
Diachronic: across time