In a moral sense, lifeless denotes a want of vital energy; inanimate, a want of expression as to any feeling that may be possessed; dull implies a torpor of soul which checks all mental activity; dead supposes a destitution of feeling.

Webster's Revised Unabridged Dictionary (1913)

Example sentences

boring The show was so boring that Ann and I fell asleep.
soulless Oli London is a completely empty, soulless grifter.
insipid Water tastes insipid after it has been boiled.
vapid What kind of vapid comments will I get on this sentence?
inert Nitrous oxide is inert at room temperature.
torpid When it gets cold, the turtles become torpid.

Popularity over time

Word	1850 → 2019	Trend
lifeless		rising
boring		rising
soulless		rising
insipid		steady
vapid		rising
inert		falling

Use in printed books, per decade from 1850 to 2019.

By length

3 letters: dry¹, fey¹
4 letters: late¹, dead¹, gone¹, flat¹, dull¹, blah¹, drab¹
5 letters: still¹, heavy², empty², stiff¹, inert², vapid², amort
6 letters: boring², asleep², desert², wooden², static², vacant², barren², stuffy², stodgy², torpid²
7 letters: passive², expired², extinct², tedious³, dormant², defunct², insipid³, prosaic³, languid²
8 letters: deceased², departed³, solitary⁴, inactive³, deserted³, stagnant², sluggish², desolate³, soulless², immobile³, plodding², unmoving
9 letters: pointless², sedentary⁴, tasteless², inanimate⁴, lethargic³, impassive³, exanimate
10 letters: breathless², lackluster³, motionless³, unoccupied⁴, lacklustre, insensible⁴, unanimated, peopleless
11 letters: uninhabited⁵
13 letters: uninteresting⁴

The small number after each word is its number of syllables (heavy² = 2 syllables).