Ruminate
Etymology
From Latin ruminari, "to chew the cud," from rumen, "the throat or first stomach" of a cud-chewing animal. A cow that ruminates brings food back up to grind it again; the mental sense borrows that image exactly — turning a thought over and over the way an ox works its cud.
verb · /ROO-mih-nayt/
To think about something long and deeply, turning it over in the mind.
What it names
The verb for slow, repetitive reflection — and, in psychology, for the darker version where you chew the same worry over and over.
Example
He ruminated on the rejection for days, replaying the interview until the words lost all meaning.
Related idea
Ponder is deliberate, often productive thought; to ruminate can tip into the unproductive loop of dwelling on the same thing.
verb · /ROO-mih-nayt/
Of cattle, sheep, and similar animals, to bring food back up from the stomach and chew it again.
What it names
The digestive process of ruminant animals, which re-chew partly digested food known as cud.
Example
The cows lay in the shade, placidly ruminating.
Related idea
This literal sense is the source of the mental one: to ruminate on a problem is to chew it over. A ruminant like a cow contrasts with animals that digest their food only once.