I'd tried installing it via net-tools
apt-get update && apt-get install -y net-tools
but that didn't help ...
I tried/failed to remember how I'd installed it last time ....
Then I found this: -
which reminded me about the apt-cache tool: -
apt-cache search nslookup
dnsutils - Clients provided with BIND
gresolver - graphical tool for performing DNS queries
knot-dnsutils - Clients provided with Knot DNS (kdig, knslookup, knsupdate)
libbot-basicbot-pluggable-perl - extended simple IRC bot for pluggable modules
libnet-nslookup-perl - simple DNS lookup module for perl
gresolver - graphical tool for performing DNS queries
knot-dnsutils - Clients provided with Knot DNS (kdig, knslookup, knsupdate)
libbot-basicbot-pluggable-perl - extended simple IRC bot for pluggable modules
libnet-nslookup-perl - simple DNS lookup module for perl
apt-get install -y dnsutils
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
bind9-host geoip-database libbind9-160 libdns1100 libgeoip1 libirs160 libisc169 libisccc160 libisccfg160 liblwres160
Suggested packages:
rblcheck geoip-bin
The following NEW packages will be installed:
bind9-host dnsutils geoip-database libbind9-160 libdns1100 libgeoip1 libirs160 libisc169 libisccc160 libisccfg160 liblwres160
...
Setting up bind9-host (1:9.11.3+dfsg-1ubuntu1.11) ...
Setting up dnsutils (1:9.11.3+dfsg-1ubuntu1.11) ...
Processing triggers for libc-bin (2.27-3ubuntu1) ...
Setting up dnsutils (1:9.11.3+dfsg-1ubuntu1.11) ...
Processing triggers for libc-bin (2.27-3ubuntu1) ...
which nslookup
/usr/bin/nslookup
nslookup -version
nslookup 9.11.3-1ubuntu1.11-Ubuntu
Job done!!