Fortunately is the adverb form of the word fortunate meaning a good or favorable situation that happened by chance. Fortune is derived from Latin and English and is a relatively new word (compared to luckily). For example:
- I only took $20 cash with me but the medicine cost $30. Fortunately, the shop accepted digital payment.
- It rained all night. Fortunately, we had moved our car inside the garage before going to bed.
- There was a power cut in our area today. Fortunately, we had our emergency light handy.
Luckily originates from Middle Dutch. Luckily is also an adverb and also means by ‘good chance’ and is used for situations that turn out to be favorable by chance. However, the context is usually more informal and is often used to express an emotional response such as gratitude. For example,
- I took the wrong medicine yesterday. Luckily for me, there were no side effects.
- As soon as my cousin left for his hometown, it started to rain. Luckily, the buses were not delayed.
- Luckily there wasn't any drama or politics in the team I managed last month.
Did you happen to notice that all the above sentences occur as part of a casual conversation? It is more common for people to use luckily in spoken English, whereas fortunately is used more in written English.
Having said this, the two words can be used interchangeably. But it's worth noting the word fortunate is also associated with happiness or relief as the situations come about due to taking the right course of action or circumstances turned out on your favor. For example, there was an option for digital payment, or you chose to park the car inside before it rained. Sometimes, you may be in luck because of situations that are beyond your control. That’s why horoscopes always share your ‘fortune’ and you can change your ‘fortune’ by doing certain things. Luck depends on various external factors too.
Here's a quotation to finish off: “The company was almost on the verge of bankruptcy. Fortunately, they could strike a good deal with a tech giant, which saved face. Luckily, none of their employees were fired during the transition.”