tftp get

Does anyone know whether I can retrieve files within a subdirectory using tftp?

I have tried
>tftp> get abc/xyz

but I can't figure out whether the syntax is wrong or if it is even possible.

When you say you have tried it would help if you'd tell what happened.
Nevertheless, yes and no, that depends on tftpd server configuration.
Do you have access to its configuration? If yes, which directory is set as root?
Read man tftpd, might will be helpful.

Sorry if my first post in any sense does not conform with forum requirements.
Yes, that is supported by the client:
$ uname -v
FreeBSD 10.2-STABLE #0: Sun Dec 13 20:50:40 UTC 2015  root@:/usr/obj/usr/src/sys/GENERIC
$ tftp
tftp> connect
tftp> binary
tftp> get FreeBSD/Kiosk/ftp/doc.txz
Received 1429192 bytes during 0.8 seconds in 2792 blocks