A calf is a young cow. A young female cow, especially one that has not yet had a calf, is called a heifer: H-E-I-F-E-R.

VOA: special.2009.07.21

And so this is the H-F bond in HF.

所以这是氟化氢中的氢氟共价键。

麻省理工公开课 - 固态化学导论课程节选