Abstract. Let M be a number field, and W M a set of its non-Archimedean. . , pr} be a finite set of prime numbers. Let F inf be the field generated by all the p j i -th roots of unity as j → ∞ and i = 1, . . . , r. Let K inf be the largest totally real subfield of F inf . Then for any ε > 0, there exist a number field M ⊂ K inf , and a set W M of non-Archimedean primes of M such that W M has density greater than 1 − ε, and Z has a Diophantine definition over the integral closure of O M,W M in K inf .