As Well As
conjunction
及ぶ means "to reach" or "to amount to." The noun version is more like a grammar thing, as it means "as well as." Perhaps if you are reaching a certain point or certain amount, then you are adding things on. That's why this means "as well as".
Note that 及び is a term usually used in formal writing.
The reading comes from 及ぶ, so if you know that one you know that one as well as this one.
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