Constant
late Middle English (in the sense ‘staying resolute or faithful’): from Old French, from Latin constant- ‘standing firm’, from the verb constare, from con- ‘with’ + stare ‘stand’. The noun senses date from the mid 19th century.
wiktionary
From Middle English constant, from Old French constant, from Latin constantem, accusative of constans, from constare(“to stand firm”). Displaced native Old English singal.
etymonline
constant (adj.)
late 14c., "steadfast, resolute; patient, unshakable; fixed or firm in mind," from Old French constant (14c.) or directly from Latin constantem (nominative constans) "standing firm, stable, steadfast, faithful," present participle of constare"to stand together," from assimilated form of com "with, together" (see con-) + stare "to stand," from PIE root *sta- "to stand, make or be firm."
Meaning "steadfast in attachment to a person or cause" is from early 15c. Of actions and conditions, "fixed, not varying" (1540s); "continual, enduring" (1650s). Meaning "regularly recurring" is from 1817. Related: Constantly.
constant (n.)
1832 in mathematics and physics, "a quantity which is assumed to be invariable throughout," from constant (adj.), which is attested from 1753 in mathematics. The general sense "that which is not subject to change" (1856) is a figurative extension from this.
