actually 歌う doesn't mean what your textbook says

Saw 歌う on a karaoke screen and realized everyone gets this wrong. Look at the kanji. The right side is 欠 which literally means 'lack' or 'yawn'. So 歌う is actually for when you are singing badly or just humming half-heartedly. If you are actually trying to sing well, you shouldn't use it. I always use it for bad karaoke. Textbooks overcomplicate things.