内 the inside

It's NICE to be a person trapped inside George Michael's stache?

contents ★★★★☆
内 (the inside) + 容 (appearance) = 内容 (contents)

the contents (of a box or a book or whatever)

guide ★★★★☆
案 (guide/proposal) + 内 (the inside) = 案内 (guide)

a guide - usually in the form of a map, or an information kiosk. Also if a clerk shows you around a store pointing out things you might want to buy, that 's annai.

within ★★★★☆
以 (compared to) + 内 (the inside) = 以内 (within)

within xxx (as in, "I'll be there within 10 minutes!")

confidential ★★★☆☆ KIDS
内 (the inside) + 緒 (together) = 内緒 (confidential)

usually defined as 'confidential,' but that makes it sound more serious than it is - like a spy document or something. Actually, 内緒 is kind of a kids' word. "Keep this information between us two."