underestimate
verb [ T ]
uk/ˌʌndəˈrestɪmeɪt/ usto think that something is or will be smaller, easier, less extreme, or less important than it really is:
The company sorely underestimated demand and is struggling to expand output.
Court interpreters say the skills required to do the job are underestimated.
to think that someone is worse at doing something, less intelligent, etc. than they really are:
Sometimes his modest manner led people to underestimate him.
underestimate
noun [ C ]
uk/ˌʌndəˈrestɪmət/ usan opinion that something is smaller, easier, less important, or less extreme than it actually is:
The total cost is likely to be an underestimate.
underestimation
noun [ C or U ]
I believe there is a significant underestimation of the real demand for oil from the developing world.