tweenlight
The period between dusk and nightfall; twilight.
rare, uncountable
Faith, sir, she says that Fergus has had an outforce lying in the hills yonder these three days, and waits an opportunity of surprising the fort — that they had moved down this tweenlight, and were sweeping along by the glens two hours ago; [...]
Where it comes from
From Old English twēonlēoht (“twilight”, literally “double-/doubtful-/uncertain-light”). The alternative spellings are due to a misassociation with between, erroneously interpreting tweenlight as if it were a shortening of between-light.
Adapted from the Wiktionary entry tweenlight (CC BY-SA 4.0).