Are detrius and detritus different words? What do they mean?

Its detritus, not detrius.

Detritus is defined as:

Loose fragments or grains that have been worn away from rock.

Disintegrated or eroded matter; debris.

Synonyms for detritus:

rubble

deposit

fragments

grains

leavings

scree

sediment

shavings

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Wednesday, August 16 2017
Source: http://www.thefreedictionary.com/Detrius