前天(qián tiān) - the day before yesterday in Mandarin

前天 (qián tiān) puts 前 (qián, "front, before") in front of 天 (tiān, "day"), and together they mean "the day before yesterday" - two days back from today, not one. English needs four words to say it; Mandarin needs two syllables.

Do not confuse it with 以前 (yǐqián, "before, previously"), which is a vague stretch of past time with no fixed distance from today. 前天 (qián tiān) names one specific day, the same way 昨天 (zuótiān, "yesterday") and 明天 (míngtiān, "tomorrow") do, and it slots into a sentence the same way: at the front, or right after the subject, with no preposition needed - 前天我很忙 (qián tiān wǒ hěn máng), "I was busy the day before yesterday".

Learn 前天 (qián tiān) alongside its mirror image, 后天 (hòu tiān, "the day after tomorrow"): both are built the same way, front and back either side of today, and both trip up English speakers who reach for a whole phrase where Mandarin only needs one compact word.