For the source text click/tap here: Pesachim 77
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It could enter your mind to say that since the term appointed time is not written with regard to them, these offerings do not override Shabbat or ritual impurity as do other communal offerings during their appointed times. Therefore, it teaches us that even the New Moon is called an appointed time. Rosh Chodesh is considered a Moed....
The obvious problem with Abaye’s explanation that Rosh Chodesh is also called mo’ed is that we don’t treat it as a festival in other respects.
Which leads us to review as to What makes Rosh Chodesh a woman's holiday?