[yesenadam]

"The cot–caught merger or LOT–THOUGHT merger, formally known in linguistics as the low back merger, is a sound change present in some dialects of English where speakers do not distinguish the vowel phonemes in "cot" and "caught". ...An additional vowel merger, the father–bother merger, which spread through North America in the eighteenth and nineteenth centuries, has resulted today in a three-way merger in which most Canadian and many American accents have no vowel difference in words like "palm" /ɑ/, "lot" /ɒ/, and "thought" /ɔ/."