A small introduction:
This could have been a "What is a ??? Word™" question, but I decided to give it a little twist. The first part is simply about finding out what makes the short words Tonal (although I decided later that "Notable" might be an even better description, so wherever you read "Tonal" you may also read "Notable"). The poem will help you as you go along.
Complete all tonal words below,
List their options in a row.
Numbers for letters is what you need,
They indicate what you should read.
Just take these, strike out the rest,
Now you have fulfilled your quest.
N.B.: All tonal words can be found in this English dictionary.
P.S.: Here is a text version of the picture above:
TONAL -> LUNATIC
LEACH -> SARCASM
HEAP -> SASHIMI
ROLL -> PLATEAU
VERY -> COMPLEX
RISKY -> COMPLEX
HOST -> THOUGHT
READ -> ATTEMPT
MEND -> REVISIT
ARROW -> FORTIFY
LIGHT -> WONDERS
GO -> DYNASTY
LOVE -> OUTDRAW
RACE -> PONTIFF
OLD -> COUTURE
OWN -> ANALYZE
LONG -> VOUCHER
ROOM -> ENCRYPT
STRAY -> HUNDRED
LASH -> SPECIES
RANK -> SANDBOX
ROUND -> NOTABLE
Hint:
Finding out what makes the shorter words tonal/notable is key.
Hint 2:
The tonal/notable property is related to the fact that these words are incomplete.