Built from humble "receive," not from arigatō
Itadaku is the humble counterpart of morau ("receive") and also functions as the humble verb for eating and drinking in honorific registers. Adding -masu yields the polite formula itadakimasu. Digital Daijisen, summarized on Kotobank, defines the meal interjection as something said before eating or drinking, acknowledging that one is about to receive food.
Arigatō belongs to a different moment: gratitude after a favor or, at the table, often after the meal. The sayonara guide covers another Japanese loanword whose English use does not match a one-word Japanese gloss. Itadakimasu fits the same pattern: a short phrase whose social job is narrower than a literal translation suggests.
What speakers are doing socially
Textbooks often gloss itadakimasu as "I humbly receive" or "let's eat," but the social move is acknowledging providers: cooks, hosts, farmers, and everyone in the supply chain. That is why the same root shows up in itadakimasu at the start and in gochisōsama deshita ("it was a feast") at the finish.
The phrase is usually said once per meal, often with hands together briefly, rather than repeated for each dish. Silent omission happens in very informal snacking, but a sit-down meal normally includes it.
How it differs from itadakimasu in anime subtitles
Fansubs sometimes render itadakimasu as "thanks for the food" because English lacks a single equivalent. That translation imports gratitude timing from arigatō and can confuse learners who then say arigatō before picking up chopsticks.
For seniority vocabulary at the same meal, senpai and kōhai name roles in a group, not table etiquette; honorifics on names (-san, -sensei) handle address at dinner separately from itadakimasu.