| thick(adjective, innocent, green, unfamiliar, unconscious) |
| tight-lipped(mysterious, private, reticent, taciturn, uncommunicative) |
| unacquainted(adjective, knowledge, ignorant, unaware, uneducated) |
| unadvised(adjective, smart, careless, unknowing, hermetical) |
| unbriefed(adjective, blank, ignorant, naive, unknowing) |
| unconscious(adjective, knowledge, innocent, ignorant, naive) |
| unconversant(adjective, innocent, thick, unfamiliar, unconscious) |
| uncultivated(adjective, innocent, thick, unfamiliar, unconscious) |
| uncultured(adjective, innocent, thick, unfamiliar, unconscious) |
| under the breath(expression, idiom) |
| under the rose(expression, idiom) |
| underground |
| undetected(obscure, dark, secret, unknown, hidden) |
| undisclosed(obscure, dark, secret, unknown, hidden) |
| uneducated(adjective, innocent, thick, ignorant, naive) |
| unexposed(obscure, dark, secret, unknown, hidden) |
| unfamiliar(adjective, knowledge, ignorant, unaware, uninformed) |
| unforthcoming(adjective, mysterious, private, reticent, taciturn) |
| uniformed(adverb, knowledge, ignorant, unanticipatedly) |
| uninitiated(adjective, innocent, thick, unfamiliar, unconscious) |