Meanings

an idle brain is the devil's shop

unpaired electron

unsaturated compound

unsaturated hydrocarbon

unsaturated fatty acid

dysfunction (often medical)

emotional instability

uncanny valley (hypothesis about humanoid robots)

reciprocity failure

Sincerely yours (with the nuance of "please excuse the brevity of this letter")

unsaturated bond

refractory period

impurity level

unfair business practice

infertility (esp. of plants)

infertility (esp. of animals)

irregular galaxy

uncertainty

sense of uncertainty

fasting