Even if it was well written, it would not reach the locution and therefore is not consulted in a dictionary. Otherwise, the meaning would be obvious (well, as it seems in 'every third day', it would not be so obvious). See each (indefinite adjective), third ("apocope of third"), day ("24-hour period").
* Only one "like" per meaning and day, the more "likes" the meaning will appear higher in the list
