The most common and most likely answer to this crossword clue is the 4 letter word ERST
E
R
S
T
More clues leading to the result ERST
- Hemingway, for example, casting central characters at first
- Workers' traditional housing long ago
- Formerly understood only the core elements
- What’s at heart of 23, long ago in former times
- Formerly in older style
- Regular occupants of eery site at one time
- A proportion of nostalgia-mongers thrived in the past
- Formerly Queen Street
- Twitter started contributing at an earlier time
- Part of ruler’s territory at one time
Buddy explains!

The straight part
We know that "Formerly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case formerly = erst.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ERST mean?
ERST adjective- First.
- First of all, before (some other specified thing).
- Sooner (than); before.
- Formerly, once, erstwhile.