The most common and most likely answer to this crossword clue is the 5 letter word ONION
I've seen this crossword clue in Financial Times
O
N
I
O
N
More clues leading to the result ONION
- One between legs — potential cause of tears?
- Bulb is in use – electric current running
- Vegetable, something not to be considered, on reflection? I will tuck in
- Bulb‘s working, subject to receiving current
- Love and marriage, don’t start that as it can make you cry!
- Bulb shining, one lit
- One between the legs a cause of tears?
- Bulb in contact with conductor of electricity
- Working on island on tear-jerker?
- Head provides view dismissing Greek character
Buddy explains!

The straight part
We know that "Bulb" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bulb = onion.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 ONION mean?
ONION noun- A monocotyledonous plant (Allium cepa), allied to garlic, used as vegetable and spice.
- The bulb of such a plant.
- The genus as a whole.
- A ball.
- A person from Bermuda or of Bermudian descent.