luckily
adv.used to say that something good happened by chance. You use it when you are glad about a situation that could have been worse.
adv.by good fortune or chance. Functions as a disjunct to express the speaker's positive attitude toward the event described.
“Luckily, the rain stopped before the party started.”
“I forgot my keys, but luckily my roommate was still at home to let me in.”
“The driver lost control on the icy patch, but luckily the car came to a halt just inches from the safety barrier.”
Sentence adverb — typically placed at the very beginning of a sentence followed by a comma.
While it can appear mid-sentence, it is most natural and common for this adverb to sit at the start of the sentence to modify the entire statement.
From lucky + -ly.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.