The most common and most likely answer to this crossword clue is the 5 letter word SWEAT
I've seen this crossword clue in The Guardian
S
W
E
A
T
More clues leading to the result SWEAT
- Long-serving soldier’s wife in chair
- Diligent student collects first in English — hard work!
- During a day our lot toil for little reward
- Constituency wife held for Labour
- Wife comes in behind Labour
- Worry about waste
- Opponents at table worry old soldier
- First of all supremo wants everyone actively tackling hard work
- Work hard with women in constituency
- Result of effort getting women to occupy chair
Buddy explains!

The straight part
We know that "Labour" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case labour = sweat.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 SWEAT mean?
SWEAT noun- Fluid that exits the body through pores in the skin usually due to physical stress and/or high temperature for the purpose of regulating body temperature and removing certain compounds from the circulation.
- The state of one who sweats; diaphoresis.
- (especially WWI) A soldier (especially one who is old or experienced).
- The sweating sickness.
- Moisture issuing from any substance.
- A short run by a racehorse as a form of exercise.
- Hard work; toil.
- To emit sweat.
- To cause to excrete moisture through skin.
- To work hard.
- To extract money, labour, etc. from, by exaction or oppression.
- To worry.
- To worry about (something).
- To emit, in the manner of sweat.
- To emit moisture.
- To solder (a pipe joint) together.
- To stress out.
- To cook slowly at low heat, in shallow oil and without browning, to reduce moisture content.
- To remove a portion of (a coin), as by shaking it with others in a bag, so that the friction wears off a small quantity of the metal.
- To suffer a penalty; to smart for one's misdeeds.
- To scrape the sweat from (a horse).