Possible Clues:

• 'An old silent pond / A frog jumps into the pond / Splash! Silence again,' e.g
• Short poem written in a traditional Japanese style
• Exercise in brevity
• Traditional three-liner
• Japanese poem with 17 syllables
• First of haunting autumnal images Keats used to write poem
• Poetic form with kireji
• Poem from WWI leader almost upset country
• 17-syllable Japanese verse form
• 'Remember to add / the missing 6-Down clue here / oops I forgot to'