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

That person won a battle with what has been called one of nature's fiercest creatures.

VOA: special.2011.03.15

It has been called one of the most influential nonfiction books of the twentieth century.

VOA: special.2009.10.18

He called Iran "one of the most complex national security problems" the United States has faced in his more than 40 years in government.

VOA: standard.2009.12.12