The most common and most likely answer to this crossword clue is the 5 letter word TANKA
I've seen this crossword clue in The Times
T
A
N
K
A
Buddy explains!
The straight part
We know that "Japanese poem" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case japanese poem = tanka.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TANKA mean?
TANKA noun- A form of Japanese verse in five lines of 5, 7, 5, 7, and 7 morae.
- A strong, forceful expression
- A Tibetan painting of the Buddha on fabric.
- An ethnic group of boat people in the Canton area.
- A kind of boat used in Canton, about 25 feet long and often rowed by tanka women; junk.
- A coin and unit of currency of varying value, formerly used in parts of India and Central Asia.