Icebergs ultimately breach vessel - Titanic? (4)
I believe the answer is:
vast
'titanic?' is the definition.
(both can mean very large)
'icebergs ultimately breach vessel' is the wordplay.
I cannot quite see how this works, but
'vessel' could be 'vas' (synonyms) and 'vas' is located in the answer.
A single letter 't' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for vast that I've seen before include "Gigantic" , "Extremely large or extensive" , "Unusually great" , "Of very great extent" , "Astronomical" .)