Final answer:
The answer is Haiku; it is a three-line, unrhymed, unmetered poetic form with a 5-7-5 syllable count that traditionally relates to nature or seasons.
Step-by-step explanation:
The word from the list that best fits the definition of a five-lined unrhymed poem about nature is Haiku. A Haiku is a well-known Japanese form that is three lines long, comprised of unrhymed, unmetered lines with a syllable count of 5-7-5. Traditionally, a Haiku's subject matter relates to nature or the seasons, which makes it the appropriate choice given the definition provided. While a Haiku is typically three lines, not five, it is the only option given that specifically relates to nature.