Numbers 10:10
Also in the day of your gladness, and in your appointed seasons, and in your new moons, ye shall blow with the trumpets over your burnt-offerings, and over the sacrifices of your peace-offerings; and they shall be to you for a memorial before your Elohim: I am Yahovah your Elohim.

Nehemiah calls the New Moon day "holy day".

Nehemiah 10: 31, 33
31 And if the people of the land bring ware or any victuals on the sabbath day to sell, that we would not buy it of them on the sabbath or on the holy day: and that we would leave the seventh year, and the exaction of every debt. ...
32 And the people  of  the land, the ones bringing merchandise and any food on day the Shabat to sell, not we would take from them on Shabat and on day holy (6944) Qodesh-dedicated, hallowed.
33 For the shew-bread, and for the continual meal offering, and for the continual burnt-offering, of the sabbaths, of the new-moons, for the set appointed times, and for the holy things.

Below-revised - New Moon instead of Shabat, because no mention is made about work, and because the fourth commandment declares the New Moon day (chodesh) to be quodesh or "Holy".

Isaiah 58:13

If you turn away from The New Moon, your foot, to do what you please, on Day My Holy, and call To New Moon, a delight, To The Holiness of Yahovah, glorified; and shall glorify It away from doing your own ways, from finding your own pleasure, or  speaking (your) word:

Is this the day of our gladness, coming before The Father Most High, and as His little children, rejoicing, eating the new fruit of the Tree of Life? Being refreshed from resting the previous Sabbath the day before, or two days before.

Ezekiel 46:3
Likewise the people of the land shall worship at the door of this gate before Yahovah in the sabbaths and in the new-moons.

Isaiah 58:14
14 Then shalt thou delight thyself in Yahovah; and I will cause thee to ride upon the high places of the earth, and feed thee with the heritage of Yacob thy father: for The Mouth of Yahovah hath spoken [it].

6942 qadash, kaw-dash'; a prim. root: to be (causat, make, pronounce or observe as) clean (ceremonially or morally):--appoint, bid, consecrate, dedicate, defile, hallow, (be keep) holy (-er, place), keep, prepare, proclaim, purify, sanctify (-led one, self) X wholly.

6944 qodesh, ko'-desh; from 6942; a sacred place or thing; rarely abstr. sanctity:-- consecrated (thing), dedicated (thing), hallowed (thing), holiness, (X most) holy (X day, portion, thing), saint, sanctuary.

2320 chodesh {kho'-desh} Hebrew: noun masculine

from 2318;(chadash-kahw-dash'  ; a prim. root; to be new; caus. to rebuild: renew, repair.)

Possible Definitions:
1) the new moon, month, monthly
1a) the first day of the month
1b) the lunar month

Strong's # 6942. xxx qadash, kaw-dash'; a prim. root; to be (causat. make, pronounce or observe as) clean (ceremonially or morally):--appoint, bid, consecrate, dedicate, defile, hallow, (be, keep) holy (-er, place), keep, prepare, proclaim, purify, sanctify (-ied, one, self), X wholly.