Second, not first number is samey (8)
I believe the answer is:
monotone
'samey' is the definition.
I can't judge whether this definition defines the answer.
'second not first number' is the wordplay.
'second' becomes 'mo' (both are short periods of time).
'first number' becomes 'one' (I've seen this in another clue).
'mo'+'not'+'one'='MONOTONE'
'is' is the link.
Can you help me to learn more?
(Other definitions for monotone that I've seen before include "Utterance at a single unvaried level" , "Sound of unchanging pitch" , "Flat and unchanging in pitch" , "Flat voice" , "Dull delivery" .)