Pole loses ice, melting first (9)
I believe the answer is:
isosceles
'first' is the definition.
Both the answer and definition are adjectives. Perhaps they are linked in a way I don't understand?
'pole loses ice melting' is the wordplay.
'pole' becomes 's'.
'melting' indicates anagramming the letters.
's'+'loses'+'ice'='slosesice'
'slosesice' with letters rearranged gives 'ISOSCELES'.
(Other definitions for isosceles that I've seen before include "Of triangular, with two sides of equal length" , "(Of triangles) having two sides the same" , "Triangle with two sides of equal length" , "Describing a triangle with two equal sides" , "Kind of triangle" .)