(v.) to be silently angry
When you’re enraged but keep your opinions silently or stubbornly to yourself, then you’re subirascing.
That’s a word that dates from the eighteenth century in English, but has its roots in its much older Latin equivalent, subirascere. That Latin word is typically glossed as ‘to be quite angry’—or, as the Oxford English Dictionary puts it, ‘to be rather annoyed’.
The prefix sub– is what’s doing the work here: derived from the Latin for ‘under’ or ‘close to’, in this context it serves just to weaken the root verb irasci, ‘to anger’ (the root of our word irascible), to give us a word meaning merely to be almost—or figuratively ‘beneath’—full outspoken rage.
So how does that give us a word meaning to silently seethe with anger? The silent part of this word appears to be an English development, seemingly implied by the image of being enraged but not quite enraged enough to speak out.
Better just to keep your opinions to yourself, then—or if you’re lucky, to let your silence and tacitness communicate your anger for you.