All about the kanji, part 2: 一

一 is the easiest kanji of them all, both to draw and to remember the meaning of. The kun reading is ひと- or ひとつ (the default counter) and the on reading is the familiar いち. So far, no surprises.
But here are some unexpected uses or pronunciations of this kanji:

• 一日中 = いちにちじゅう, which means 'throughout the day', even though the individual kanji mean one, day, and inside or middle.
• 一緒に = いっしょに, which means 'together'. The kanji 緒 can mean strap, cord or even thong, so it literally reads 'in one strap', which I guess is 'bound together'.
• 一昨日 = おととい, meaning the day before yesterday, where 昨日 means yesterday
• 一から = いちから means 'from the beginning', 'from the top' (literally 'from one').
• 一生懸命 = いっしょうけんめい, 'with utmost effort', where the next kanji mean life/birth, suspend/depend/hang, and destiny/fate.

And let's not forget the recently learned いちばん, literally 'number one', which is used to say that something is the fastest, coolest, slowest etc.
一 is also very often pronounced as just い or いっ when used in combination with a specific counter, such as　いっぱい, one cupful (of, say, beer).