T.S. Eliot popularized the term objective correlative, which orginally was coined by Washington Allston in 1840. Simply explained, it is the use of a symbol to "describe" generally inexplicable concepts like color or emotion. I first came across the concept when I sat in on a phone interview of poet Rachel Zucker, who was a fan of using objective correlatives in her poetry:
many cities no longer exist
but there is cleaning to finish
lemon halves wrapped
in clinging plastic (Eating in the Underworld, pg. 11)
Lemon is acerbic, bitter, clean, stinging, yellow...lemon conveys so many emotions, feelings, and concepts.
What are some things that symbolize fear? Longing? Desire? Go work five into your novel.