To define multiple keywords you should use the '/k' command which accepts a string with hexa scaped characters. Here's an example of use:
[0x08048000]> /k0 lib
[0x08048000]> /k1 rt
[0x08048000]> /k ; list introduced keywords
00 lib
01 rt
To search these two keywords just use the '/r' (ranged search) command:
[0x08048000]> /r 0-1
001 0x00000135 hit0_0 lib/ld-linux.so.2
002 0x00000b71 hit0_1 librt.so.1__gmon_st
003 0x00000b74 hit1_2 rt.so.1__gmon_start
...