Columns layout

The -c display the words on a line in column. The end-of-line characters, if any, are honored.

This example shows what happens in column mode:

smenu -c

The same with the arrows in bold red (-a option)

smenu -a s:1,b -c

And now, here's what happens when the cursor is moved to a hidden word.

This is a general concept: the arrows show that there are more words in the direction they indicate.