expression
half out of interest; mostly out of curiosity
Used when someone does something motivated partly by curiosity, often implying it's not a serious or committed reason. Commonly used in the adverbial form 興味半分で.
興味半分でその本を読み始めたが、結局最後まで読んでしまった。
I started reading the book half out of curiosity, but ended up finishing it.
彼は興味半分にその機械をいじってみた。
He tinkered with the machine half out of curiosity.
Compound of 興味 (interest) and 半分 (half). The expression is transparently derived from its components.