The most common and most likely answer to this crossword clue is the 4 letter word LIFE
I've seen this crossword clue in Financial Times
L
I
F
E
More clues leading to the result LIFE
- Very long sentence in biography
- Long sentence in biography?
- Long sentence in biography
- Desperately important to correct daft headline
- Being made of lithium and iron
- Provided the central of this sentence
- Sentence from a biography
- Existence of metals
- Long sentence in novel, I feel
- Sentence, one foot in length, cut by two thirds
Buddy explains!

The straight part
We know that "Sentence/a biography" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sentence/a biography = life.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 LIFE mean?
LIFE noun- The state of organisms preceding their death, characterized by biological processes such as metabolism and reproduction and distinguishing them from inanimate objects; the state of being alive and living.
- The animating principle or force that keeps an inorganic thing or concept metaphorically alive (dynamic, relevant, etc) and makes it a "living document", "living constitution", etc.
- Lifeforms, generally or collectively.
- A living individual; the fact of a particular individual being alive. (Chiefly when indicating individuals were lost (died) or saved.)
- Existence.
- A period of time during which something has existence.
- Animation; spirit; vivacity.
- A biography.
- Nature, reality, and the forms that exist in it.
- An opportunity for existence.
- The life insurance industry.
- A life assured under a life assurance policy (equivalent to the policy itself for a single life contract).