| Undercover, informally | 22 |
| Undercover worker, perhaps | 26 |
| Undercover police operation | 27 |
| Undercover group: Abbr. | 23 |
| Undercover drug agents | 22 |
| Undercover cop, perhaps | 23 |
| Undercover cop, at times | 24 |
| Undercover cop of 1970s TV | 26 |
| Undercover agent, in slang | 26 |
| Undercover agent's wear | 27 |
| Undercover agent's cover? | 29 |
| Undercover agent of a sort | 26 |
| Undercooked, as an egg | 22 |
| Undercooked meat danger | 23 |
| Underconfident utterances | 25 |
| Undercoat applications | 22 |
| Undercard fight, for short | 26 |
| Underbosses' bosses | 23 |
| Underappreciated laborer | 24 |
| Underage temptation, slangily | 29 |
| Underage drinker's item | 27 |
| Underage drinker in Lincoln? | 28 |
| Underachiever's motto? | 26 |
| Under-water detection aid | 25 |
| Under-the-window routine | 24 |
| Under-the-window performance | 28 |
| Under-the-weather-looking | 25 |
| Under-the-table things | 22 |
| Under-the-table promotion | 25 |
| Under-the-table payments | 24 |
| Under-the-table payment | 23 |
| Under-the-table flirtation | 26 |
| Under-the-table diversion | 25 |
| Under-the-table activity | 24 |
| Under-the-table action | 22 |
| Under-the-sink scourers | 23 |
| Under-the-sink installation | 27 |
| Under-the-sink cleaners | 23 |
| Under-the-hood cleaner | 22 |
| Under-the-gun situations | 24 |
| Under-the-cushions find | 23 |
| Under-the-chin helmet securer | 29 |
| Under-the-abdomen area | 22 |
| Under-one's-breath sound | 28 |
| Under-21 request, sometimes | 27 |
| Under, at the hospital | 22 |
| Under ___ (securely shut in) | 28 |
| Under wraps, so to speak | 24 |
| Under what circumstances | 24 |
| Under way, to Sherlock Holmes | 29 |
| Under way, to Sherlock | 22 |
| Under way, as racehorses | 24 |
| Under the ___ (nautical term) | 29 |
| Under the weather, e.g. | 23 |
| Under the table, maybe | 22 |
| Under the sea, to poets | 23 |
| Under the name of, as a co. | 27 |
| Under the mattress, maybe | 25 |
| Under the effects of Novocain | 29 |
| Under the cloak of night | 24 |
| Under present conditions | 24 |
| Under political attack, maybe | 29 |
| Under optimum conditions | 24 |
| Under one's protection | 26 |
| Under one's guidance | 24 |
| Under one's control | 23 |
| Under one's command | 23 |
| Under one's charge | 22 |
| Under no circumstances | 22 |
| Under ideal circumstances | 25 |
| Under Helios's influence | 28 |
| Under favorable circumstances | 29 |
| Under different circumstances | 29 |
| Under Cupid's spell | 23 |
| Under covers for the night | 26 |
| Under control, in a way | 23 |
| Under any circumstances | 23 |
| Under a false name, briefly | 27 |
| Under 32 degrees Fahrenheit | 27 |
| Undependable group member | 25 |
| Undemonstrative to the max | 26 |
| Undemocratic government | 23 |
| Undelivered by the P.O. | 23 |
| Undeliverable piece of mail | 27 |
| Undeliverable letters: Slang | 28 |
| Undefinitive statement | 22 |
| Undecided, you might say | 24 |
| Undecided, on a TV schedule | 27 |
| Undecided, in an angsty way | 27 |
| Undecided's oxymoron | 24 |
| Undecided's abbreviation | 28 |
| Undecided courtroom group | 25 |
| Undealt portion of the deck | 27 |
| Uncurved, as test scores | 24 |
| Uncultivated, probably | 22 |
| Unctuous, flattering speech | 27 |
| Uncritically enthusiastic | 25 |
| Uncritical learning style | 25 |
| Uncredited credit, in quotes | 28 |
| Uncredited cast member | 22 |