Guilty means having actually done the thing — the opposite of innocent. Found guilty, guilty of theft, plead guilty. It is the word a court uses and the word a conscience uses.
The two senses need keeping apart. Legally guilty is a finding: a jury decides it. Feeling guilty is an emotion and needs no crime at all — I feel guilty about not phoning. The preposition differs too: guilty of a crime, guilty about a feeling. Note the useful phrase a guilty pleasure, meaning something you enjoy and are slightly embarrassed by, and guilty conscience, which is what makes people explain things nobody asked about.
1adjectiveguiltyHaving committed a crime or done wrong.
“He was found guilty on all four counts.”
synonyms: culpable, at fault
2adjectivefeelingFeeling bad about something you did.
“She felt guilty for a week about not going.”
3adjectiveshowingShowing that you know you did wrong.
“He had a guilty look on him from the doorway.”
Too few real examples of this word to estimate which sense is commonest.
guilty is a state of fault.
Old English gyltig comes from gylt, a crime or a debt owed — and the debt sense is the older one. Guilt has always been something you owe for what you did, which is why it can be discharged, carried, and felt long after the debt is paid.
Old English
gyltiġ — offending, guilty
Middle English
gilty
English, today
guilty
From Middle English gilty, gulty, from Old English gyltiġ (“offending, guilty”); equivalent to guilt + y.
Etymology from Wiktionary, CC BY-SA