deprimi

Not de- plus a root primi. There is no verb primi in Esperanto, so the de- you can see at the front is not the Esperanto preposition doing prefix duty - it is Latin de- frozen inside a word that came over whole. Deprim- is one root. The same is true of deprimo and deprimiĝi: they are built on that root, not on a root prim-.

Register, honestly. English has let "depressed" slide between a clinical diagnosis and a wet Tuesday, and Esperanto has inherited some of that slide. On this site the everyday sense is what the examples teach - weather, news, a long grey week - because that is what learners need to say. The medical condition has its own word, depresio, and clinicians use it precisely; if you mean the illness, use depresio rather than stretching deprimo. Saying mi estas deprimita about a bad afternoon is normal Esperanto and nobody will read it as a diagnosis, but knowing that the two words exist separately is the difference between speaking loosely and speaking carelessly.

The forms. Deprimi is transitive - a thing depresses a person. Deprimiĝi is to become low, and deprimita is the adjective for the person: li estas deprimita, he is down. Deprima describes the cause: deprima vetero, depressing weather. Deprimo is the low mood itself.

Nearby. Malĝoja is plain sadness. Tedi is to bore. Ĝeni is to bother. Konsoli is what you do about any of them, and it is a kinder verb to reach for than most learners realise.