primacy n.

late 14c., "first, original, first in order of time," from Old French prime and directly from Latin primus "first, the first, first part," figuratively "chief, principal; excellent, distinguished, noble" (source also of Italian and Spanish primo), from Proto-Italic *prismos, superlative of PIE *preis- "before," from root *per- (1) "forward," hence "in front of, before, first, chief."

The meaning "of fine quality, of the first excellence" is from c. 1400. The meaning "first in rank, degree, or importance" is from 1610s in English. Arithmetical sense (as in prime number, one indivisible without a remainder except by 1) is from 1560s; prime meridian "the meridian of the earth from which longitude is measured, that of Greenwich, England," is from 1878. Prime time originally (c. 1500) meant "spring time;" the broadcasting sense of "peak tuning-in period" is attested by 1961.

word-forming element making nouns of quality, state, or condition, a confusion in English of three similar suffixes from Latin:

1. in primacy, etc., from Old French -acie and directly from Medieval Latin -acia, Late Latin -atia, making nouns of quality, state, or condition from nouns in -as.

2. in advocacy, etc., from Late Latin -atia, forming nouns of state from nouns in -atus.

3. in fallacy, etc., from Latin -acia, forming nouns of quality from adjectives in -ax (genitive -acis). Also forming part of -cracy. It has been extended in English to nouns not found in Latin (accuracy) and to non-Latin words (piracy).

"state of being concealed; secretive habits, want of openness," 1570s, a variant of secretee, "quality of being secret" (early 15c.), from Middle English secre (adj.), from Old French secré, variant of secret (see secret (adj.)) + -ty (2). The alteration of form is perhaps on the model of primacy, etc. In the same sense secretness is from early 15c.; secreness from late 14c.