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)

歓心を買う[kanshinwokau] to win favour
競争売買[kyousoubaibai] auction
故買[kobai] buying stolen goods
購買[koubai] procurement
購買力[koubairyoku] buying power

思惑買い[omowakugai] speculative buying
衝動買い[shoudougai] impulsive buying
人身売買[jinshinbaibai] slave trade
人買い[hitokai] slave traffic
青田買い[aotagai] speculatively buying a rice harvest, while the fields are still green