> a few letters

Any time until 13 February you can look up any words beginning with this week's letter, or with any of the previous letters of the week.

PLUS!
For 48 hours after each programme (from 22:00 GMT on Mondays to 22:00 GMT on Wednesdays) you can look up any words, beginning with any letter, in the whole of the OED.

[e.a.]