JMdictProject
commented
4 months ago A page is being developed on the project Wiki which covers these tags, The text of this issue has been transferred there. See: https://www.edrdg.org/wiki/index.php/Kanji_and_Reading_Information_Fields
[An "issue" is being opened for each of the kanji/reading tags to provide a forum for discussing the definitions and criteria for applying the tags. It is intended to be used to assist in the preparation of documentation of the tags.]
The [oK] tag is associated with kanji forms and is currently defined as "Word containing out-dated kanji or kanji usage". It is currently used in 700 entries. It probably should be redefined as "form containing a kyūjitai/old character form" or something similar. (This has been discussed in issue #103.)
The purpose of the tag is to inform users that one or more of the kanji in the surface form is of an older variety (旧字体 or similar) and that forms using more recent kanji (e.g. 新字体) are in use. An example is the 合気道/合氣道 entry, where the 合氣道 form is tagged as [oK]. Other kanji pairs which could lead to use of the tag include 国/國, 学/學 and 竜/龍.