| Uncut gem | 9 |
| Uncut ruby, e.g. | 16 |
| Undamaged | 9 |
| Undated? | 8 |
| Undaunted | 9 |
| Undead flesheater | 17 |
| Undead in the water? | 20 |
| Undealt portion of the deck | 27 |
| Undebatable subject | 19 |
| Undeceived | 10 |
| Undecided | 9 |
| Undecided courtroom group | 25 |
| Undecided person | 16 |
| Undecided's abbreviation | 28 |
| Undecided's oxymoron | 24 |
| Undecided, as a jury | 20 |
| Undecided, in a way | 19 |
| Undecided, in an angsty way | 27 |
| Undecided, in some listings (abbr.) | 35 |
| Undecided, on a TV schedule | 27 |
| Undecided, you might say | 24 |
| Undecided: Abbr. | 16 |
| Undeclared | 10 |
| Undecorated | 11 |
| Undecorated type? | 17 |
| Undefeated boxer, or her father | 31 |
| Undefeated coll. 11 in '82 | 30 |
| Undefiled | 9 |
| Undefined | 9 |
| Undefined amount | 16 |
| Undefined mathematical operation | 32 |
| Undefined penalty | 17 |
| Undefinitive statement | 22 |
| Undeleted expletive | 19 |
| Undeliverable letter | 20 |
| Undeliverable letter, in post-office talk | 41 |
| Undeliverable letter, to a postal worker | 40 |
| Undeliverable letters: Slang | 28 |
| Undeliverable piece of mail | 27 |
| Undelivered by the P.O. | 23 |
| Undeluded about | 15 |
| Undemanding | 11 |
| Undemanding classes | 19 |
| Undemanding courses | 19 |
| Undemanding, as a job | 21 |
| Undemocratic decree | 19 |
| Undemocratic government | 23 |
| Undemocratic law | 16 |
| Undemocratic tendency | 21 |
| Undemocratic types | 18 |
| Undemonstrative to the max | 26 |
| Undeniable | 10 |
| Undeniable facts | 16 |
| Undeniable success | 18 |
| Undeniable truth | 16 |
| Undeniably | 10 |
| Undependable | 12 |
| Undependable group member | 25 |
| Undependable person | 19 |
| Under | 5 |
| Under to poets | 15 |
| Under 100 mg per deciliter of this is considered optimal | 56 |
| Under 20, to most | 17 |
| Under 21 | 8 |
| Under 32 degrees Fahrenheit | 27 |
| Under a ban | 11 |
| Under a black cloud | 19 |
| Under a canopy | 14 |
| Under a cloud | 13 |
| Under a false ID | 16 |
| Under a false name, briefly | 27 |
| Under a jinx | 12 |
| Under a microscope | 18 |
| Under a parasol, e.g. | 21 |
| Under a parasol, say | 20 |
| Under a quilt, say | 18 |
| Under a spell | 13 |
| Under a stopwatch | 17 |
| Under a strain | 14 |
| Under a whammy | 14 |
| Under an assumed name, briefly | 30 |
| Under an assumed name, informally | 33 |
| Under an elm | 12 |
| Under an umbrella | 17 |
| Under anesthetic | 16 |
| Under any circumstances | 23 |
| Under any conditions | 20 |
| Under attack | 12 |
| Under attack, perhaps | 21 |
| Under canvas | 12 |
| Under challenge | 15 |
| Under circumstances? | 20 |
| Under class man? | 16 |
| Under close scrutiny | 20 |
| Under closer | 12 |
| Under command | 13 |
| Under confinement | 17 |
| Under consideration | 19 |
| Under control | 13 |
| Under control across the board | 30 |