c. 1300, from Anglo-French grevous (Old French grevos) "heavy, large, weighty; hard, difficult, toilsome," from grief (see grief). Legal term grievous bodily harm attested from 1803.
1540s, "influential, respected; marked by weighty dignity," from French grave (Old French greve "terrible, dreadful," 14c.), from Latin gravis, "heavy, ponderous, burdensome, loaded; pregnant;" of matters, "weighty, important;" of sounds, "deep, low, bass;" figuratively "oppressive, hard to bear, troublesome, grievous," from PIE root *gwere- (1) "heavy."
In English, the sense "solemn, sober" is from 1580s; of immaterial things, "important, serious" 1590s. Greek barys (opposed to kouphos) also was used figuratively, of suffering, sorrow, sobbing, and could mean "oppressive, burdensome, grave, dignified, impressive." The noun meaning "accent mark over a vowel" is c. 1600, from French.
early 15c., "arranged in sequence, continuous" (a sense now obsolete); mid-15c., of persons, "expressing earnest purpose or thought, resolute," from Old French serios "grave, earnest" (14c., Modern French sérieux) and directly from Late Latin seriosus, from Latin serius "weighty, important, grave."
This is probably from a PIE root *sehro- "slow, heavy" (source also of Lithuanian sveriu, sverti "to weigh, lift," svarus "heavy, weighty;" Old English swær "heavy," German schwer "heavy," Gothic swers "honored, esteemed," literally "weighty").
According to Middle English Compendium, two sets of Latin stems "seem to have fallen together" in Medieval Latin: ser- (as in series, serere) and sēr- (as in sērius, sēriōsus, etc.), perhaps through semantic overlap, which accounts for the earlier Middle English record of the word, which seems to belong to the first stem.
As "in earnest, not pretending or jesting," from 1712; in reference to of music, theater, etc., "dealing with grave matters" by 1762. The meaning "attended with danger, giving grounds for alarm" is from 1800. Serious-minded is attested by 1845.
1806, gooroo, from Hindi guru "teacher, priest," from Sanskrit guru-s "one to be honored, teacher," from guru- "venerable, worthy of honor," literally "heavy, weighty," from PIE root *gwere- (1) "heavy." Generalized sense of "mentor" is from 1940 (in H.G. Wells); sense of "expert in something" first recorded c. 1966 in Canadian English in reference to Marshall McLuhan.
c. 1400, "thick;" early 15c., "heavy, weighty, clumsy by reason of weight," from Latin ponderosus "of great weight; full of meaning," from pondus (genitive ponderis) "weight," from stem of pendere "to hang, cause to hang; weigh" (from PIE root *(s)pen- "to draw, stretch, spin"). From late 15c. as "important." Meaning "tedious" is first recorded 1704. Related: Ponderously; ponderousness; ponderosity (1580s in the figurative sense).
early 13c., "hardship, suffering, pain, bodily affliction," from Old French grief "wrong, grievance, injustice, misfortune, calamity" (13c.), from grever "afflict, burden, oppress," from Latin gravare "make heavy; cause grief," from gravis "weighty" (from PIE root *gwere- (1) "heavy"). Meaning "mental pain, sorrow" is from c. 1300. Good grief as an exclamation of surprise, dismay, etc., is from 1912.
late 14c., oracioun, "a prayer," from Late Latin orationem (nominative oratio) "a speaking, speech, discourse; language, faculty of speech, mode of expressing; prayer," noun of action from past-participle stem of Latin ōrare "to pray to, plead, speak before an assembly" (see orator). The usual Old French form was oraison. Meaning "formal speech, discourse, eloquent or weighty address" is recorded from c. 1500.
"absent in mind, distracted from present reality by intellectual activity," 1640s, past-participle adjective from abstract (v.). Related: Abstractedly.
An absent man is one whose mind wanders unconsciously from his immediate surroundings, or from the topic which demands his attention; he may be thinking of little or nothing. An abstracted man is kept from what is present by thoughts and feelings so weighty or interesting that they engross his attention. [Century Dictionary]