兌換[dakan] conversion (of paper money, esp. into specie)
兌換銀行[dakanginkou] bank of issue

兌換券[dakanken] convertible banknotes

クーポン券[kuuponken] coupon (ticket)
グリーン券[guriinken] green (car) ticket
ビール券[biiruken] beer coupon
会員券[kaiinken] membership card
回数券[kaisuuken] book of tickets

割引券[waribikiken] discount coupon or ticket
株券[kabuken] stock certificate
急行券[kyuukouken] express ticket
金券[kinken] gold certificate

アナログデジタル変換器[anarogudejitaruhenkanki] analog-digital converter
データ交換[deetakoukan] data exchange
パリティ変換[paritihenkan] parity transformation (physics)
メール交換[meerukoukan] exchange of letters
意見交換[ikenkoukan] exchange of ideas

引換て[hikikaete] on the contrary
下位互換性[kaigokansei] downward compatibility
かな漢字変換[kanakanjihenkan] kana-kanji conversion (on a computer, etc.)
可換群[kakangun] Abelian group
賀詞交換[gashikoukan] New Year greetings (parties)