Account for cross appearing in strange alpine (7)
I believe the answer is:
explain
'account for' is the definition.
(thesaurus)
'cross appearing in strange alpine' is the wordplay.
'cross' becomes 'x'.
'appearing in' indicates putting letters inside.
'strange' indicates an anagram.
'alpine' with letters rearranged gives 'eplain'.
'x' inserted inside 'eplain' is 'EXPLAIN'.
(Other definitions for explain that I've seen before include "Show the meaning of, make clear" , "offer clarification" , "Justify" , "Make understandable" , "Give reasons for" .)