The English language, like many others, has numerous expressions that focus on a single word yet the expressions themselves have different meanings. Here are few. Feel free to add your own in the comments section below.

First things first. This phrase is typically used when organising one's affairs and is often used at the beginning of a sentence. Its essential meaning is "Let's prioritise".

Once you've gotten your plan together and you have an idea of what you want to do, you'll then consider when you actually want to implement this plan. As it's never a good idea to procrastinate, especially when you have your priorities all right, the best time is probably first thing. This expression is normally used to refer to early in the day and used in the context of getting something done first thing in the morning. In other words, this has to be the very first thing on your agenda that you set out to do. It can also be heard where there is a sense of urgency and the act must be performed without delay.

First off has a similar meaning but is probably less formal and implies that something has to be done immediately or at the outset. It is really another way of saying "firstly" or "first of all".

First hand is another expression that can cause the non-native English speaker difficulty. If you come to know of something "first hand", it means you discovered it from the original source, from someone who directly experienced the incident, for instance.

Further expressions incorporating "first" include to cast the first stone. Someone who casts the first stone is someone who is quick to judge, normally the person who is first to condemn another who has done wrong.

Our final expression using "first" is love at first sight which is most likely the most understood by English learners. If you experience "love at first sight" it means you are attracted romantically to someone from the first time you saw them.