Think of duck with a soft ending stuck on it. The easiest picture to hold is a small yellow duck: round, light, harmless, and slightly funny to look at. That ending, -y, is the same one in kitty and doggy, and it makes whatever it touches sound smaller and friendlier. The supplied source splits the word into two — one from the bird on the water, one from duck used as a pet name for a person — but both leave the same taste behind: small, soft, and easy to like.
From the word’s history
The supplied source gives several etymology trees, all of them duck + -y: duck the bird plus -y, duck the bird plus the diminutive -y, and duck used as a term of endearment plus the diminutive -y.
來源列了好幾條詞源樹，全都是 duck 加上 -y：一條是「鴨子 + -y」，一條是「鴨子 + 表示小的 -y」，還有一條是「duck（暱稱）+ 表示小的 -y」。所以這個字從頭到尾就是在一個 duck 上加一層「小而親暱」的外衣，只是加在不同意思的 duck 上。
Wiktionary, "ducky" (etymology 1)
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