c. 1400, "pre-eminence, magnificence;" early 15c., "greatness of size or extent," from Latin magnitudo "greatness, bulk, size," from magnus "great" (from suffixed form of PIE root *meg- "great") + -tudo, suffix forming abstract nouns from adjectives and participles (see -tude).
Meaning "size, extent," whether great or small is from early 15c. Of stars, "brightness or brilliancy expressed as a number" (now on a logarithmic scale) from 1640s, translating Ptolemy's Greek megethos.
First attested in phrases such as heir apparent (see heir). Meaning "superficial, spurious" is from c. 1400; that of "appearing to the senses or mind but not necessarily real" is from 1640s. Apparent magnitude in astronomy (how bright a heavenly body looks from earth, as opposed to absolute magnitude, which is how bright it really is) is attested from 1875. Middle English had noun forms apparence, apparency, but both are obsolete from 17c.
c. 1500, "loftiness, height," from French grandeur, from Old French grandor "size, height, extent, magnitude; greatness" (12c.), from grand "great" (see grand (adj.)). "Being a word of late adoption, it retains the Fr. form -eur of the suffix." Extended sense of "majesty, stateliness" in English is first recorded 1660s.
"in which smoking is not permitted," 1905; the sign wording itself is attested by 1817.
Smoking is a vice to [sic] — and a national one, of such magnitude that railroad corporations throughout all their routes in the United States, have a special command in large letters, conspicuously placed at depots and inside of the cars — "No smoking allowed here." ["The Sailor's Magazine," December 1840]
1530s, "a reduction in rank or dignity," from French dégradation (14c., Old French degradacion), noun of action from past-participle stem of degrader (see degrade). From 1752 as "state of being reduced from a higher to a lower grade or power;" by 1769 as "reduction of strength, value, magnitude, etc." Related: Degradational.
"quantity having magnitude and direction," 1846; earlier "line joining a fixed point and a variable point," 1704, from Latin vector "one who carries or conveys, carrier" (also "one who rides"), agent noun from past-participle stem of vehere "carry, convey" (from PIE root *wegh- "to go, move, transport in a vehicle"). Related: Vectorial.