/ˈpɜːrfɪktli/
[adverb] In a way that is complete, correct, or without any faults. It can also mean 'completely' or 'absolutely', as in 'perfectly clear'.
The word 'perfectly' carries the idea of something that has been 'thoroughly made' — finished so completely that nothing is missing.
The story of 'perfectly' begins in ancient Latin, with the verb 'facere', meaning 'to make' or 'to do'. This verb combined with the prefix 'per-', meaning 'through' or 'thoroughly', to create 'perficere', meaning 'to carry through to completion' or 'to finish entirely'. From this verb came the past participle 'perfectus', describing something that had been fully completed — not merely good, but genuinely finished, with nothing left undone.
From Latin, the word passed into Old French as 'parfit' and later 'parfait', still carrying the sense of something brought to its fullest possible state. English speakers borrowed this word in the 13th and 14th centuries, and it gradually settled into the spelling we use today: 'perfect'. The adverb form 'perfectly' followed naturally, adding the common Old English suffix '-lice' (which became '-ly' in modern English), meaning 'in the manner of'.
What is striking about the word's original meaning is how concrete it was. 'Perfect' did not originally mean 'very good' or 'excellent' in a vague, flattering sense. It meant specifically 'completed' — something that had reached its intended end. A perfect circle was not just a nice circle; it was a circle that had been drawn all the way around, with its beginning and end meeting precisely. This explains why the grammatical term 'perfect tense' refers to actions that have been fully completed, as in 'I have finished' rather than 'I am finishing'.
Over the centuries, the meaning of 'perfect' broadened and softened. Because things that are truly finished and complete tend also to be things without errors, the word shifted to mean 'flawless' or 'without fault'. By the time 'perfectly' became common in everyday English speech during the 15th and 16th centuries, it was used both in its original sense of completeness and in its newer sense of excellence or flawlessness. Shakespeare and his contemporaries used it freely in both ways.
In modern English, 'perfectly' has stretched even further, becoming a general intensifier. When someone says 'that is perfectly fine' or 'I am perfectly happy', they are not really talking about flawlessness at all — they simply mean 'completely' or 'absolutely'. This journey from a precise Latin engineering term meaning 'thoroughly made' to a casual word we use to emphasise almost anything is a wonderful example of how language softens and expands over time, becoming more flexible but sometimes losing its original sharpness.