The word “Astrophage” occurs 556 times in Project Hail Mary (including in the plural).

The word is coined by Grace in 03.260 based on “Greek and Latin root words” in response to Stratt’s question: “What would you call an organism that exists on a diet of stars?”

Both Latin and Greek have cognates of astro- and -phage meaning ‘star’ and ‘eater’ respectively: The Greek ἄστρον means ‘star’ and Greek φαγεῖν ‘to eat or devour’ (hence also φάγος, ‘glutton’). The -phage suffix is also found in biological terms like ‘polyphage’, ‘macrophage’, or ‘bacteriophage’.

In the novel, “Astrophage” is always capitalized and, in three occurrences, when displayed on a screen is in ALL-CAPS.

There is some inconsistency, even by the narrator, as to whether “Astrophage” is a mass or count noun. And even when a count noun, there’s inconsistency in whether there is a separate plural form.

For example, in 04.036 Grace, as narrator, says “Stratt still insisted I be the only person to look at Astrophage” where it’s presumably a mass noun (although just from this could be a plural without a separate form). Earlier in 04.026, Grace, as narrator, says “Astrophage can propel itself” so it appears unambiguously to be a mass noun.

However, in 04.037 Grace says “The ambient temperature of an Astrophage is 96.415 degrees Celsius” with the indefinite article, treating it as a count noun.

In 04.041, he says “I put some Astrophage in ice-cold water for an hour” which could be a mass noun or a plural without separate form but then, in the next sentence he says “When I pulled them out, they were 96.415 degrees Celsius.” which makes it a plural count noun with a singular form.

But we do see an actual plural form 4 times: ”my Astrophages” (05.031), “millions of little Astrophages” (09.077, spoken by Dimitri), “my little Astrophages” (09.103), and “trillions and trillions of horny little Astrophages” (19.204).

It is notable that the qualifier “little” also appears in three out of four cases. In two cases, there is an actual count which may have primed the use of the plural form. It is interesting that, in the other two cases, the possessive “my” is used, although there are other cases with singular form (mass noun) “my Astrophage” so this just seems to be an inconsistency.

Here’s a visualization of the relative frequencies across all sections and chapters of the book.