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!