dull (adj.)

c. 1200, "stupid, slow of understanding, not quick in perception;" also, of points or edges, "blunt, not sharp;" apparently from Old English dol "dull-witted, foolish," or an unrecorded parallel word, or from Middle Low German dul "foolish, reckless," both from Proto-Germanic *dulaz (source also of Old Frisian dol "reckless," Middle Dutch dol, dul "stupid, foolish, crazy," Old Saxon dol, Old High German tol "foolish, dull," German toll "mad, wild," Gothic dwals "foolish").

This sometimes is conjectured to be from PIE *dhul-, from root *dheu- (1) "dust, vapor, smoke," which also produced words for "defective perception or wits, turbidity of the mind" (compare Greek tholos "mud dirt," Old Irish dall "blind").

Dull. Ineffective for the purpose aimed at, wanting in life. A dull edge is one that will not cut ; a dull understanding, does not readily apprehend ; a dull day is wanting in light, the element which constitutes its life ; dull of sight or of hearing is ineffective in respect of those faculties. [Wedgwood]

From late 12c. as a surname. Rare before mid-14c. Of color "not bright or clear," from early 15c.; of pain or other sensations, "not sharp or intense," from 1725. Sense of "not pleasing or enlivening, uninteresting, tedious" is from c. 1400. Related: Dullness.

dull. (8) Not exhilarating; not delightful; as to make dictionaries is dull work. [Johnson]

dull (v.)

c. 1200, "to lessen the vigor, activity, or sensitiveness of" (transitive), from dull (adj.). Of pointed or edged things, "make less sharp, render blunt," from late 14c. Of colors, glass, etc., "remove the brightness or clearness of," late 14c. Intransitive sense of "lose vigor, intensity, or keenness" is from late 14c. Related: Dulled; dulling.

Definitions of dull
dull (adj.)
(of color) very low in saturation; highly diluted;
dull greens and blues
dull (adj.)
lacking in liveliness or animation;
a dull political campaign
how dull and dreary the world is
he was so dull at parties
fell back into one of her dull moods
a large dull impassive man
dull days with nothing to do
dull (adj.)
emitting or reflecting very little light;
a dull sky
a dull glow
dull silver badly in need of a polish
dull (adj.)
being or made softer or less loud or clear;
the dull boom of distant breaking waves
Synonyms: muffled / muted / softened
dull (adj.)
so lacking in interest as to cause mental weariness; "what an irksome task the writing of long letters is"- Edmund Burke; "the tiresome chirping of a cricket"- Mark Twain;
his competent but dull performance
a dull play
Synonyms: boring / deadening / ho-hum / irksome / slow / tedious / tiresome / wearisome
dull (adj.)
not keenly felt;
dull pain
a dull throbbing
dull (adj.)
slow to learn or understand; lacking intellectual acuity; "although dull at classical learning, at mathematics he was uncommonly quick"- Thackeray;
Synonyms: dense / dim / dumb / obtuse / slow
dull (adj.)
(of business) not active or brisk;
business is dull (or slow)
Synonyms: slow / sluggish
dull (adj.)
not having a sharp edge or point;
the knife was too dull to be of any use
dull (adj.)
blunted in responsiveness or sensibility; "so exhausted she was dull to what went on about her"- Willa Cather;
a dull gaze
dull (adj.)
not clear and resonant; sounding as if striking with or against something relatively soft;
the dull thud
Synonyms: thudding
dull (adj.)
darkened with overcast;
a dull sky
Synonyms: leaden
dull (v.)
make dull in appearance;
Age had dulled the surface
dull (v.)
become dull or lusterless in appearance; lose shine or brightness;
the varnished table top dulled with time
dull (v.)
deaden (a sound or noise), especially by wrapping;
Synonyms: muffle / mute / damp / dampen / tone down
dull (v.)
make numb or insensitive;
Synonyms: numb / benumb / blunt
dull (v.)
make dull or blunt;
Too much cutting dulls the knife's edge
Synonyms: blunt
dull (v.)
become less interesting or attractive;
Synonyms: pall
dull (v.)
make less lively or vigorous;
Middle age dulled her appetite for travel