intercident
Coming or falling between; happening accidentally.
obsolete
But it is found by ſad experience, that ſhe rouſes herſelf up to make a criſis, not only upon improper, and, as phyſicians call them, intercident days, […] vvhich ſeldom afford any criſis, and much ſeldomer a good one; but alſo vvhen there appear not any ſigns of coction, or at leaſt of due coction, and by theſe unſeaſonable attempts vveaken the patient, and increaſe the malady, or perhaps make it ſpeedily mortal.
Where it comes from
From Latin intercidens, intercedentis, present participle of intercidere (“to fall between”); inter (“between”) + cadere (“to fall”).
Adapted from the Wiktionary entry intercident (CC BY-SA 4.0).