姻 is a Logical Aggregate and Phonetic Compound at the same time, formed from two semantic indicators of 女 (literally means a female, woman) and因(literally means an evening; a dusk) and 因 (yīn, with the same pronunciation) is also defined as its phonetic component.
结亲的男家，女婿家family of son-in-law, family of a woman’s husband
Lily explains 姻 like this:
If you’ve already followed us through the previous lessons of “安" and “因", you will be able to understand “姻" with much ease. For in Confucian thought, a woman was born for her husband and child instead of for her own clan or herself. It is her husband and her husband’s family that she should be dedicated to and rely on through all her life. Remember that “因" originally means a straw mat or cushion on the ancient Chinese carriage used for people sitting or resting on? A married woman is just like getting on a carriage of her husband’s family, where she rightly belongs and totally relies on as well.
I'm shckoed that I found this info so easily.
You've got it in one. Co'dnlut have put it better.