Japanese nouns can be combined to create new nouns. When combining nouns, the first kana in the second noun should be in γ γγ¦γ (dakuten) form if one is available.1
Example: Pocket-watch
γγγ‘γ γγ©γγ
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γγγ‘γ γ refers to the inside of ones pocket.
γ©γγ is γ¨γγ (clock) with the first kana in γ γγ¦γ form. Together these nouns make βpocket-watchβ (or more exactly, βpocket-clockβ).