a week tomorrow, on Monday, etc.

a week (tomorrow/on Monday/Tuesday/etc.)

One week from the day specified. Primarily heard in UK. I'm flying to Ireland a week on Saturday for my brother's wedding. We need that report finished a week tomorrow.
See also: Monday, on, Tuesday, week

a ˌweek toˈmorrow, on ˈMonday, etc.

(British English) (also a ˌweek from toˈmorrow, ˈMonday, etc. American English, British English ) seven days after the day that you mention: It’s my birthday a week on Tuesday.
See also: on, week