Attention, notice, or awareness; the state of directing one's mind toward something.
From Latin 'advertentia' (attention, care) via 'advertent' (attentive), with the '-cy' suffix. This is essentially a variant of 'advertence,' both developed in English to represent the abstract quality of paying attention.
Both 'advertency' and 'advertence' mean the same thing, but 'advertency' is used more in philosophy and theology, while 'advertence' appears more in modern English—showing how synonyms can drift into different specialized contexts.
Complete word intelligence in one call. Free tier — 50 lookups/day.