All about the kanji, part 7: 大

Image: giant jellyfish off the coast of Japan.
If 人　is a person, then as 大, he or she has outstretched arms, indicating a big size. That is why 大 means big. kun reading is おおー or おおきい (also the adjective); on reading is たい　or だい (the beginning of 大学 or　だいがく, 'big school', that is, university.
Some compounds with kanji we already know:

• 大人 = おとな, adult;
• 国大 = こくだい, national university (here 大 is short for 大学)
• 大国 = たいこく, large country (duh) but also 'the great powers'
• 大会 = たいかい, mass meeting, rally, convention

What's very unusual (maybe even unique) about the adjective derived from this kanji is that there are two:

• 大きい (おおきい), an i-adjective; and
• 大きな (おおきな), a na-adjective

Both mean the same thing and can, as far as I know, be used interchangeably.