|General Commands Manual
dnsname - does a reverse lookup for the IP address
dnsname does a reverse lookup for the IP address a.b.c.d. It prints the first domain name for that address. If no domain names are listed in DNS, dnsname prints a blank line. You can list several IP addresses; dnsname prints each result on a separate line.
There is also a dnsfilter(1) program that reads IP addresses from its input and performs many reverse lookups in parallel.
Normally dnsname exits 0. If dnsname encounters a temporary problem that prevents it from determining the domain name, it prints an error message and exits 111.