Half-tide doesn't sound right to me, slack-tide is something else entirely, my google-fu has failed me.
I don't claim expertise, but after living in four different coastal areas of three different bodies of water, I've not heard one. It's always just "6 hours to high tide" or something like that, they want to know time to high/low point so people can plan accordingly.
“Stand of the tide” is offered by Wikipedia: https://en.wikipedia.org/wiki/Slack_tide?wprov=sfti1#Misconceptions
Stand of the tide seems different than the midpoint. At the midpoint the tide is definitely changing in one direction or another.
Stand of the tide seems maximum or minimum.
Idk the answer to your question, but it seems like there should be one. Equitide or something.
Ebb is the state of the tide going out, Flow is coming in.
Intertidal is an interesting thought, but isn't it already taken by the area that is covered by high tide and exposed at low.
