| อุดมคติ | ooL dohmM khaH dtiL | noun | ideals; principles |
อุดมคตินิยม | ooL dohmM khaH dtiL niH yohmM | noun | idealism |
อุดมสมบูรณ์ | ooL dohmM sohmR buun[n]M | adjective | fertile; abundant; plentiful |
| อุดร | ooL daawnM | noun, adjective | the north; northern |
| proper noun, geographical | Udon; in northeast Thailand |
| อุดรธานี | ooL daawnM thaaM neeM | proper noun, geographical | Udon Thani, a province in northeastern Thailand with a 1995 population of 1,456,154 (rank 8 of 76) |
| อุดหนุน | ootL noonR | | to aid (with money); help |
| อุดหู | ootL huuR | phrase | to block (up) (one's) ears; [i.e.] to wear earplugs |
| อุดอู้ | ootL uuF | adjective, phrase, colloquial | [of the weather and feeling] stuffy |
| อุตดม | ootL dohmM | adjective | best; most excellent |
| noun | (state of) excellence; (condition of) best quality |
| adjective | abundant |
| อุตพิด | ootL phitH | noun | stinkweed, Thlaspi arvense |
| อุตรดิตถ์ | ootL dtaL raH dit[t]L | proper noun, geographical | Utaradit, a province in northern Thailand with a 1995 population of 476,997 (rank 51 of 76) |
| อุตรนิกาย | ootL dtaL raH niH gaaM yaH | noun | Uttaranikaya; Mahayana sect of Buddhism |
| อุตราวัฎ | ootL raaM watH | verb, intransitive | to rotate in the left or counter-clockwise direction |
| อุตสาห์ | ootL saa[h]R | adjective | diligent; industrious; persistent |
| verb | to act diligently; to act industriously; to act persistently; to apply oneself |
| อุตสาหกร | ootL saa[h]R gaawnM | noun | industrialist |
| อุตสาห์กรรม | ootL saa[h]R gamM | noun | industry |
| อุตสาหกรรม | ootL saa[h]R gamM | noun | industrial enterprise; industry; industrial undertaking |
| อุตสาหกรรมการผลิต | ootL saa[h]R gamM gaanM phaL litH | noun | manufacturing industry |
| อุตสาหกรรมท่องเที่ยว | ootL saa[h]R gamM thaawngF thiaaoF | noun | the tourist industry |
| อุตสาห์กรรมบันเทิง | ootL saa[h]R gamM banM theerngM | noun | the entertainment industry |
| อุตสาห์กรรมยา | ootL saa[h]R gamM yaaM | noun, phrase, formal | drug or medicine industry |
| อุตสาหการ | ootL saa[h]R gaanM | noun | industrial technology |
| อุตสาหะ | ootL saaR haL | | [see อุตสาห์] |
| อุตุนิยม | ooL dtooL niH yohmM | noun | meteorology |
| อุตุนิยมวิทยา | ooL dtooL niH yohmM witH thaH yaaM | noun | [the study of] meteorology |
| อุท | ootL | noun, Pali, Sanskrit | water |
| adverb, Pali, Sanskrit | ahead; before; beyond |
| อุทก | ooL thohkH | noun, loanword, Pali, Sanskrit | [relating to] water; aqua-; hyrdo- |
| อุทกวิทยา | ooL thohkH witH thaH yaaM | noun | hydrology |
| อุทธรณ์ | ootL thaawn[n]M | verb, formal | to make a legal appeal |
| อุทธัจ | ootL thatH | noun, adjective, Pali | pride; arrogance; haughtiness |
| noun | confusion; distraction; fantasy |
| อุทบาตร | ootL baat[r]L | noun | water pot |
| อุทยาน | ooL thaH yaanM | noun | garden; park; national park |
| อุทยานแห่งชาติ | ooL thaH yaanM haengL chaatF | noun, phrase, formal | National Park |
| อุทยานแห่งชาติเขาใหญ่ | ooL thaH yaanM haengL chaatF khaoR yaiL | proper noun, geographical, phrase | Khao Yai National Park |
| อุทยานแห่งชาติตะรุเตา | ooL thaH yaanM haengL chaatF dtaL rooH dtaoM | proper noun, geographical, phrase, formal | the Tarutao National Park in the southern province of สตูล (Satun) |
| อุทร | ooL thaawnM | noun, Pali | abdomen; stomach; gut; bowel; womb; internal cavity |
| อุทัย | ooL thaiM | noun | sunrise |
| อุทัยธานี | ooL thaiM thaaM neeM | proper noun, geographical | Uthai Thani, a province in northern Thailand with a 1995 population of 324,730 (rank 65 of 76) |
| อุทาน | ooL thaanM | verb, intransitive | to exclaim or interject |
| noun | [grammar] an exclamation or interjection |
| อุทานเสริมบท | ooL thaanM seermR bohtL | noun | [a word in Thai grammar which acts as a euphonious or decorative suffix] |
| อุทิศ | ooL thitH | verb | dedicate; devote (to); donate (to) |
| อุทิศตน | ooL thitH dtohnM | verb | to dedicate onself |
| อุทุมพร | ooL thoomM phaawnM | noun | Udumvara tree, Ficus glomerate |
| อุธรณ์ | ooL thaawn[n]M | | [alternate spelling of อุทธรณ์] |
| อุ่น | oonL | verb | to warm up; to heat slowly |
| attributive verb | [is] warm |
| verb | [ทำให้อุ่น] to heat or reheat |
| attributive verb | [อุ่นใจ] [is] (feeling) secure; happy; at ease |
| noun | [ความอุ่น] [relief] comfort; relief; contentment |
| อุ่นใจ | oonL jaiM | attributive verb | [is] (feeling) secure; happy; at ease |
| อุบ | oopL | verb | to conceal; keep secret |
| verb | to keep; hold back |
| อุบไต๋ | oopL dtaiR | verb | to hold back; to keep a secret |
อุบล  | ooL bohnM | proper noun, geographical, colloquial | Ubon [short form of Ubon Rajathanee] |
| noun | [ดอกอุบล] lotus; water lily |
| noun, proper noun | Ubol [a Thai female name] (water lilly, lotus) |
| อุบลรัตน์ | ooL bohnM rat[n]H | proper noun, person | [เจ้าฟ้าหญิงอุบลรัตน์] H.R.H Royal Princess Ubol Ratana |
