The root verb here is इ which belongs to 2nd conjugation parasmaipada. The meaning is to go. When prefix anu is added to a verb, it changes the meaning of the word to do it after. In this case to go after i.e. follow. Additionally, when the prefix sam is added, it chages the meaning of the verb to do that act properly. In this case, to follow somebody properly or succeed like succeesion of the prince to the throne after the king. so all taken together the meaning of samanvaya is to succeed or obey or apply.
Please also note many sanskrit words which are in use in many indian languages today have not retained their original meaning. e.g. dharma in any indian language means religion. But in Sanskrit, it is used to mean duty not religion.
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