The most common and most likely answer to this crossword clue is the 7 letter word GENESIS
I've seen this crossword clue in The Times
G
E
N
E
S
I
S
More clues leading to the result GENESIS
- Army officer is putting opponents in the book
- Book is on units of heredity
- What we inherit with lives beginning
- Book, on reflection, somewhat overemphasises negativity
- Start rock band
- Information is needed about European society’s origin
- Start doing the Mexican wave as Mardi Gras ends
- Eugene’s Israelite carrying part of Torah
- See sign involved creative act
- Simmons abandoned Kiss, heading off with British rock band
Buddy explains!

The straight part
We know that "Start" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case start = genesis.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 GENESIS mean?
GENESIS noun- The origin, start, or point at which something comes into being.