Tunisia’s capital missing from book of maps, regrettably (4)
I believe the answer is:
alas
'regrettably' is the definition.
('alas' is said before regrettable information)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for alas that I've seen before include "Sad to say!" , "Lackaday" , "Sadly, unfortunately" , "Oh dear!" , "Regretfully!" .)