Compounds of

• エロ
  (adj-na,n,adj-no) erotic
  eroticism
  (P)
• オア
  (n) (comp) OR
• オケ
  (n) (abbr) orchestra
  (P)
• オタ
  (n,suf) (col) (abbr) nerd
  geek
  enthusiast
• オフ
  (n) off
  (P)
• オペ
  (n) (abbr) medical operation
  (P)
• オン
  (n,vs) on
  (P)
• カー
  (n) car
  (P)
• カウ
  (n) (comp) (abbr) automatically responding with an upload slot to someone who allows you to download (e.g. in P2P systems)
• カキ
  (n) kaki
  Japanese persimmon (Diospyros kaki)
• カジ
  (n) (uk) paper mulberry (Broussonetia papyrifera)
• カゼ
  (n) (abbr) casein
• カツ
  (n) (abbr) cutlet
  (P)
• カバ
  (n) (uk) birch (esp. Japanese white birch)
• カバ
  (n) (uk) hippopotamus (Hippopotamus amphibius)
• カバ
  (n) kava (Piper methysticum)
  kavakava
• カビ
  (n) mold
  mould
  mildew
• カブ
  (n) cub
  (P)
• カム
  (n) cam
  (P)
• カヤ
  (n) (uk) Japanese nutmeg tree (Torreya nucifera)
• カ月
  (ctr) (number of) months
  (P)
• カ行
  (n) classification for Japanese verb with the dictionary form ending in "ku"
  "ka" column or row of the kana syllabary
• カ国
  (ctr) counter for countries
• カ氏
  (n,adj-no) degrees Fahrenheit
• カ所
  (n) passage
  place
  point
  part
• カ変
  (n) (abbr) irregular conjugation (inflection, declension) of the verb "kuru"
• ガー
  (n) gar (any fish of family Lepisosteidae)
  garfish
  garpike
• ガイ
  (n) guy
  (P)
• ガキ
  (n) (1) (uk) brat
  kids
  (2) (Buddh) preta (hungry ghost)
  ghoul
• ガサ
  (n) (sl) household search (conducted by the police)