New road in London's opening first, say? (7)
I believe the answer is:
ordinal
'first say?' is the definition.
(first is a kind of ordinal)
'new road in london's opening' is the wordplay.
'new' indicates an anagram.
'opening' says to take the initial letters.
The initial letter of 'londons' is 'l'.
'road'+'in'='roadin'
'roadin' with letters rearranged gives 'ordina'.
'ordina'+'l'='ORDINAL'
(Other definitions for ordinal that I've seen before include "Old Iran (anag)" , "Eg second" , "Relating to position in a sequence" , "Ranking number" , "Roman Catholic service book" .)