tisike (Middle English) comes from Latin phthisicus, from Ancient Greek φθισικός, from Ancient Greek φθίσις, from Proto-Hellenic kʷʰtʰítis, from Proto-Indo-European dʰgʷʰítis, from Proto-Indo-European dʰgʷʰey- — to decline; to perish.
tisike (Middle English): phthisis, phthisic