undefinable
1. [ adjective ] not capable of being precisely or readily described; not easily put into words
Synonyms: indefinable
Examples:

"an indefinable feeling of terror" "an abstract concept that seems indefinable"

Related terms: undefined
Similar spelling:   undefined
  undefiled
  undefendable
  uneatable
  undependable
  undependably
  undefeated
  unadvisable
  unadoptable
  unadaptable