GG5: 〔斎戒〕 fasting; a fast; votive abstinence; 〔厄日に引きこもること〕 confinement to one's house on unlucky days.

abstention != abstinence

@@ -25 +25 @@
-<gloss>purification through fasting and abstention</gloss>
+<gloss>purification through fasting and abstinence</gloss>

https://ejje.weblio.jp/content/物忌み
役者は一定の期間別火（べっか）という物忌みを行う（特に女性と同じ火を使うことを忌む）。例文帳に追加
Actors engage in Monoimi (purification through fasting and abstention) called Bekka (literally, "separate fire," during which they cook with sacred fire, avoiding unclean fire used by others, particularly women) for a period of time.

https://ja.wikipedia.org/wiki/物忌み
斎戒に同じ　(we gloss 斎戒 as "purification").
具体的には、肉食や匂いの強い野菜の摂取を避け、他の者と火を共有しないなどの禁止事項がある。日常的な行為をひかえることには、自らの穢れを抑える面と、来訪神 (まれびと)などの神聖な存在に穢れを移さないためという面がある。
Wikipedia further says the modern prescription is:
「潔斎して身体を清め、衣服を改め、居室を別にし、飲食を慎み、思念、言語、動作を正しくし、汚穢、不浄に触れてはならない」

https://d-museum.kokugakuin.ac.jp/eos/search/?contents_type=93&pageID=5
From the evening of March first the gūji (head priest) and shinshoku (shrine priests) enter into a period of monoimi (purificatory abstinence) 


A Mysterious World within Japan: Kyoto Seimei Shrine
http://goinjapanesque.com/11734
Monoimi (物忌み): To stay confined in one’s home for a certain period of time to avoid calamity.

Specifies onmyoudo for [2]:
https://kobun.weblio.jp/content/物忌み
陰陽道（おんようどう）で日や方角が悪いとされるときに、一定期間、家にこもって心身を慎むこと。

The Characteristics of On'yōdō and Related Texts [article]
Yamashita Katsuaki Joseph P. Elacqua
Cahiers d'Extrême-Asie  Année 2012  21  pp. 79-105
https://www.persee.fr/doc/asie_0766-1177_2012_num_21_1_1392
In addition, these texts explain days designated as "monoimi" (days of taboo), during which one must sequester themselves at home in order to avoid misfortune.

sankoku(one combined sense): 食事や行い、また、外出を慎んで、体が汚れないようにする (avoid impurities)

Maybe this has some limited ritualistic practice in modern times, but this appears to be mostly a Heian period activity.  Makes an appearance in the Tale of Genji, which increases its visibility.

For sense[2], references are consistent in specifying a period of time, not necessarily a single day. "Sequestering to one's house" can, it seems, be a part of sense[1], but to the extent that 物忌み is specifically about staying home on unlucky days, seems to be an onmyoudo related activity.  We have lots of xrefs to 陰陽道 for practices related to it.

I like the first ref's suggestion of "abstention" over "abstinence".  All sources I've seen seem to indicate a much broader restriction on activities (and human interaction) than the nuance of "abstinence" would seem to imply.  It's also a short-term restriction during ritual periods (not the long-term nuance often associated with abstinence)

@@ -25,2 +25 @@
-<gloss>fasting</gloss>
-<gloss>abstinence</gloss>
+<gloss>purification through fasting and abstention</gloss>
@@ -32 +31,2 @@
-<gloss>confinement to one's house on an unlucky day</gloss>
+<xref type="see" seq="1170530">陰陽道</xref>
+<gloss>confinement to one's house on inauspicious days to avoid misfortune (Onmyōdō practice)</gloss>

mk

@@ -23,0 +24 @@
+<pos>&vi;</pos>
@@ -25,0 +27,5 @@
+</sense>
+<sense>
+<pos>&n;</pos>
+<pos>&vs;</pos>
+<pos>&vi;</pos>

koj

@@ -7,0 +7,3 @@
+<k_ele>
+<keb>物忌</keb>
+</k_ele>
@@ -9,0 +12,8 @@
+</r_ele>
+<r_ele>
+<reb>ものいまい</reb>
+<re_restr>物忌</re_restr>
+</r_ele>
+<r_ele>
+<reb>ぶっき</reb>
+<re_restr>物忌</re_restr>