Wiktionary
think on
vb. (context transitive archaic English) To think about; to meditate concerning.
Usage examples of "think on".
I said, trying to think on my feet and be ready to run with them, too.
Her energy and hope and life transforming that black place and time into something unique, something I think on the verge of holy.
When I think on these wondrous things, even spiritual comfort whatsoever it be becometh sore weariness to me.