Mountain break with sea view oddly lacking (7)
I believe the answer is:
everest
'mountain' is the definition.
(thesaurus)
'break with sea view oddly lacking' is the wordplay.
'break' becomes 'rest' (rest is a kind of break**).
'with' says to put letters next to each other.
'oddly lacking' means one should take alternating letters.
'sea'+'view'='seaview'
The alternating letters of 'seaview' are 'eve'.
'rest' put after 'eve' is 'EVEREST'.
(Other definitions for everest that I've seen before include "Mount, climbed 1953" , "High mountain" , "Himalayan mount" , "One conquered in 1953" , "Himalayan peak" .)