遅い
おそい
osoi
= late (time) / slow (speed)
Osoi is the single antonym that covers both ‘late’ and ‘slow’ in Japanese — the reverse of hayai’s two-kanji split. Whether you’re talking about arriving late to a meeting or a slow internet connection, osoi (遅い) handles both, making it simpler to learn than its counterpart but equally important to understand in context.
Osoi (遅い) is an i-adjective meaning both ‘late’ (in terms of time) and ‘slow’ (in terms of speed or pace). Unlike English, which uses different words for lateness and slowness, Japanese uses the single word 遅い for both: 帰りが遅い (kaeri ga osoi, coming home late), バスが遅い (basu ga osoi, the bus is slow / late), 動きが遅い (ugoki ga osoi, the movement is slow). Context usually makes the meaning clear. Osoi can also describe a slow thinker, a slow metabolism, or a delayed reaction. The adverb form is osoku (遅く): osoku made hataraku (遅くまで働く, working until late).
遅刻 (chikoku, tardiness) is the formal noun for being late to school or work and carries more social gravity than simply osoi. Saying ‘chikoku shimashita’ (遅刻しました, I was late) to a teacher or boss acknowledges a failure to meet expectations. In Japanese train culture, 電車が遅れています (densha ga okurete imasu — ‘the train is delayed’) is common over the PA system, using the verb okureru (遅れる) rather than the adjective osoi. For internet speed, osoi (遅い) is the natural informal complaint: ‘Wi-Fi ga osoi!’ (Wi-Fiが遅い！ — ‘the Wi-Fi is slow!’).
遅い is written with 遅 (chi/osoi), which contains the movement radical 辶 combined with 犀 (rhinoceros). The rhinoceros component historically suggested heaviness and deliberateness of movement, contributing to the meaning of slowness. The character 遅 appears in 遅延 (chien, delay — as in 列車遅延, ressha chien, train delay), 遅刻 (chikoku, being late / tardiness), and 遅速 (chisoku, slow speed — used in technical contexts).
Everyday use
今日は帰りが遅くなりそうです。先に食べてください。
Kyou wa kaeri ga osoku narisou desu. Saki ni tabete kudasai.
I’ll probably be home late today. Please eat without me.
Casual / Social Media
このアプリ、動作が遅すぎてイライラする。
Kono apuri, dousa ga osoisugite iraira suru.
This app is so slow it’s frustrating.
Formal / Cultural context
遅刻は社会人として許されないことだと心得てください。
Chikoku wa shakaijin to shite yurusarenai koto da to kokoroete kudasai.
Please understand that being late is unacceptable as a working adult.
The cultural weight of osoi in Japan is significant because of how seriously lateness (遅刻, chikoku) is treated in professional and educational settings. Japanese schools typically have strict rules about 遅刻, and a single late arrival can require a formal apology and official documentation. This reflects broader social expectations around punctuality as a form of respect (気遣い, kizukai) toward others. The counterintuitive result is that Japanese people often arrive early precisely to avoid the social cost of being even slightly osoi.
The overlap of ‘late’ and ‘slow’ in a single word (遅い) is linguistically interesting because it reflects how the concepts are connected at a more fundamental level than English separates them. A slow person (動きが遅い, ugoki ga osoi) and a late person (来るのが遅い, kuru no ga osoi) share the same kanji because both involve a deficit relative to expected timing or pace. This unified concept becomes apparent in the verb form 遅れる (okureru, to be delayed / to fall behind), which applies equally to trains running late, individuals arriving after the expected time, and technological progress lagging behind other countries.