A thousand in the back rank came into view (7)
I believe the answer is:
emerged
'came into view' is the definition.
(I've seen this in another clue)
'a thousand in the back rank' is the wordplay.
'a thousand' becomes 'M' (Roman numeral for a thousand).
'in' indicates putting letters inside.
'the back' says the letters should be written backwards.
'rank' becomes 'degree' (synonyms).
'degree' reversed gives 'eerged'.
'm' inserted inside 'eerged' is 'EMERGED'.
(Other definitions for emerged that I've seen before include "Came out, became known" , "Came forth" , "Transpired" , "Slowly came out" , "Came into view or became apparent" .)