The one and only Tim Bowen is back with another interesting word grammar discussion for Your English.
Only is a versatile word, functioning as an adverb, an adjective and a conjunction. As an adverb it can generally be replaced by the word just, as in the following examples: It's only an idea; She was only 18 when she had her first child; I only hope we can finish this on time. Used as an adjective it means that there are no other things or people of the same kind as the ones that you are mentioning, as in: This is the only letter my father ever wrote to me; I was an only child; You are the only person who can help me. As a conjunction it can replace but, as in: Fiction is like real life, only better; You can come, only make sure you’re on time; Her car is like mine, only it has four doors.
It can also be used to show that someone or something is the best, as in: Flying is the only way to travel; In my opinion, he is the only man for the job. Together with just, it can be used to mean a short time ago (The film’s only just started, so you haven’t missed much.) and to indicate by a small amount or degree (We are only just managing to satisfy the demands of our customers).
Only + infinitive is used to say that what follows is disappointing or unpleasant, as in I opened the box, only to discover that some of the parts were missing and We arrived at the pub, only to find it was closed.
The phrase only too + an adjective can be used to mean very when you wish that the situation was different (We are only too aware of the problems with this particular product) or to say that you are very willing to do something (I'd be only too happy to show you round the offices).