The mantras are from the Taittiriya Upanishad, Shikshavalli I.20 that says: matrudevo bhava, pitrudevo bhava, acharyadevo bhava, atithidevo bhava. It genuinely connotes "be one for whom the Mother is God, be one for whom the Father is God, be one for whom the Teacher is God, be one for whom the guest is God." matrudevah, pitrudevah, acharyadevah, atithidevah are single word each, and each one is a Bahuvrihi samasta-pada
Tithi in Sanskrit shows a (calendrical) date. In old times, when strategy for correspondence were confined and it was unreasonable for guests to imagine their date of landing, atithi (which really means "without a settled calendrical time") was composed to depict a meeting person who had no modified date of section or flight. Devah (which, through sandhi or euphonic blend, gets the chance to be formed/insisted as devo when taken after by particular sorts of consonants) means God and bhava means Be or Is - "be the one for whom the Guest is God"