Keywords, Ad Groups, or Campaigns may show a label of either [enabled] or [disabled].
Disabled keywords are those keywords of the campaign/ad group which are currently being reported by Amazon as paused, archived or blocked.
Keywords may be reported by Amazon as "disabled" for one of the following reasons:
All search terms attached to the keyword are negative-matched.
The equivalent keyword co-exists in the same ad group yet is archived (eg. 2 of the same keyword in different status)
The ad group is paused.
The campaign is paused (within the recent 24 hours).
The portfolio is paused.
The keyword is paused.
In the case of a temporarily-paused campaign (e.g. "day parting"/time of day tactic), you may select Settings > Account Settings > Settings > Show Archived / Paused Campaigns to make such campaigns/ad groups/keywords visible and editable.