Coded message in one page held by singer (6)
I believe the answer is:
cipher
'coded message' is the definition.
(I've seen this in another clue)
'one page held by singer' is the wordplay.
'one' becomes 'I' (Roman numeral).
'page' becomes 'p'.
'held by' means one lot of letters goes inside another.
'singer' becomes 'cher' (Cher is a US musician).
'i'+'p'='ip'
'ip' placed into 'cher' is 'CIPHER'.
'in' is the link.
(Other definitions for cipher that I've seen before include "Key to a code" , "Symbol representing nought, thing of no importance" , "nobody" , "Code - 0" , "Person or thing of no importance, or the symbol 0" .)