Week

A week was a period of time equal to seven days.

The young Jeanne-Antoinette Poisson remarked she had not seen the Tenth Doctor in weeks when he visited her in 18th century France. (TV The Girl in the Fireplace)

The Human-Hath War on Messaline lasted seven days, or "just a week" as Donna Noble put it. (TV: The Doctor's Daughter)