the.com/odor

your most ancient sense, hardwired to memory before language ever showed up

means A smell, especially a distinct or strong one that the nose picks up from the air.

from Straight from Latin 'odor,' meaning smell or scent, which came into English through Old French 'odor.' The same root breathes through 'odorous,' 'malodorous,' and 'deodorant,' and it's likely a distant cousin of Greek 'ozein' (to smell) and even 'ozone,' that sharp electric tang named for its noticeable reek.

smell map: Humans distinguish roughly one trillion distinct scents
memory hijack: Olfactory nerves wire straight into emotion centers
fingerprint: Your personal scent is as unique as DNA
detection: Dogs smell some compounds at parts per trillion
phantom whiffs: Phantosmia makes brains invent smells that aren't there

for instance

durian fruit — southeast asian fruit banned on public transport in singapore and thailand for its pungent sulfurous smell

ammonium sulfide — chemical compound used in leather tanning that produces the rotting egg smell, detected at parts per billion

thioacetone — organic compound synthesized in 1889 that caused mass evacuation in freiburg, germany when traces escaped the lab

trimethylamine — compound in fish that causes the characteristic fishy odor, measured in aquaculture and food spoilage detection