Other forms: congratulated, congratulating, congratulates
To congratulate someone is to tell them you are glad about the good thing that has happened to them. A handshake after the exam results, a card when the baby arrives, a message the evening someone gets the job.
The preposition is ON, and learners get this wrong more than any other part of the word: you congratulate her on her promotion, not for it. What you say out loud is congratulations, always with the s — congratulation on its own is not something anybody says. You can also congratulate yourself, which carries a hint of smugness: he congratulated himself on getting out early. The adjective is congratulatory, used for messages and speeches. It is a slightly formal verb; among friends people just say well done.
1verbcongratulateTo tell someone that you are pleased about their success, luck or happy news.
“Everyone stopped to congratulate her on the new job.”
2verbfeelTo feel pleased with yourself about something you have done.
“He congratulated himself on leaving before the traffic built up.”
formal in this meaning — an editor’s judgement
Congratulate came into English around 1548 from Latin congrātulor, "to wish joy, to rejoice with" — con-, "together", plus grātulor, built on grātus, "grateful, pleasing, agreeable, beloved". The heart of it is joy shared rather than praise handed down. The same grātus sits inside grateful, gratitude and grace.
Proto-Indo-European
*gʷerH-
Latin
congrātulātus
English, today
congratulate
Built from
1548; Latin congrātulātus, the perfect active participle of Latin congrātulor (“to wish joy, rejoice (with); to congratulate”) (see -ate), from con- + grātulor, from grātus (“grateful, pleasing, agreeable, beloved”) + -ō. by surface analysis, con- + gratulate.
Etymology from Wiktionary, CC BY-SA