Literally, it means “charm[-ing] animal”.
In Hebrew, compound nouns are written as separate words, with the last word in normal nominal form, and the rest in construct form. For feminine singular nouns like ’חַיָה‚=“animal”, the construct form is normally formed simply by replacing the suffix ’ה ָ ‚ with ’ת ַ ‚.
the word "חיית" is the possessive form of the word "חיה" (khaya) which means animal (another way to say animal "בעל חיים", which literally translates to owner of a life), I don't know what the word "מחמד" means, all I know is that it comes from root ח-מ-ד, which is related to "נחמד" (nice, pronounced nekhmad) and "חמוד" (cute, pronounced khamud).
Is there a written rule somewhere (DL or otherwise) for when the doubling of yod or vav or whatever else takes place? Because I know I've picked up on it incidentally, but whenever I think I've figured out the rule, I feel like I see something else that contradicts what I thought. Any help appreciated.
Thanks in advance!
There are many rules but here is the simple version.
Yod is doubled when writing without niqqud to prevent confusion. For example, ציר tsir, means hinge or axis and ציר can also mean tsayar, artist or painter. To differentiate them, צייר clearly indicates that the word is not tsir. It has more meanings than just tsayar, but you’ll come to that later.
Similarly, when writing without niqqud, a double vav helps prevent confusion. הוורד havered is “the rose”, but if you were to write it as הורד, it appears to be ho- or hu- something.
You can find out these things by googling “when is a double vav used in Hebrew?” for example.