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1. Not meant or adapted for a given purpose; inappropriate: a solvent that is unfit for use on wood surfaces.
2. Below the required standard; unqualified: an unfit parent.
3. Not in good physical or mental health.
4. Biology Unable to survive or produce viable offspring in a particular environment.
tr.v. un·fit·ted, un·fit·ting, un·fits
To cause to be unsuited or unqualified: "Having run for president ... often unfits a man for lesser or more useful subsequent work" (Garry Wills).
unsuitable: unused to and unfitted for any form of manual labour.