Interest or amusement; an older/nominal form corresponding to 'interesting' or 'funny' (modern equivalent: 面白い).
面白半分でその噂を広めてはいけない。
Don't spread that rumor just for the fun of it.
彼は小さなことでもすぐに面白がる。
He gets amused/excited by even small things.
そんな面白を追い求めるより、実務を優先しなさい。
Rather than chasing such amusements, prioritize practical work.