Paranoid means convinced that people are out to get you when nothing shows it. The colleague who reads a two-word reply as an insult, watches who is whispering by the window, and is sure the meeting he missed was about him.
The everyday use is much lighter: 'I'm paranoid about locking the door' means anxiously over-careful, not ill. The medical use is heavy — paranoid delusions, paranoid schizophrenia — and there the false belief cannot be argued away. The noun for the state itself is paranoia. The word takes ABOUT for the thing you fear and THAT for the whole suspicion: paranoid about germs, paranoid that everyone noticed. Paranoid is not a fancy word for worried; the fear is always about what other people are doing to you.
1adjectiveparanoidWrongly convinced that other people mean you harm.
“After the burglary he became paranoid about every stranger on the street.”
synonyms: suspicious, distrustful
2adjectiveanxiouslyAnxiously over-careful about something going wrong.
“I'm paranoid about missing flights, so I arrive three hours early.”
3adjectiverelatingRelating to paranoia, a mental illness in which someone holds fixed false beliefs of being persecuted.
“The clinic treats paranoid delusions with medication and therapy.”
Too few real examples of this word to estimate which sense is commonest.
Proto-Indo-European
*(s)neh₁-
Ancient Greek
παράνοια — madness
English
paranoia
English, today
paranoid
Built from
From paranoia + -oid. paranoia Ancient Greek παράνοια (“madness”), from παράνοος (“demented”), from παρά (“beyond, beside”) + νόος (“mind, spirit”). by surface analysis, para- + nous + -ia.
Etymology from Wiktionary, CC BY-SA