labor-n; 4 Senses

Sense Number 1: the activity of work, toil

Commentary: LABOR[+activity][+physical][+human][+work]
NOTE: refers to the activity of work, usually physical

John's garden is a labor of love.
Digging ditches is pure manual labor.
All their labors to bring the parties to the negotiating table were in vain.
How much labor will be involved in this undertaking?
The prisoners performed hard labor on a daily basis.
Sally doesn't like the division of labor on this project.
The airlines are trying to reduce labor costs. (Could also be Senses 3 or 4)

PropBank: labor.01
WordNet 3.0 Sense Numbers: 1, 4

Sense Number 2: the process of childbirth

Commentary: LABOR[+activity][+physical][+human][+process][+childbirth]

She had a difficult labor with her twin boys.
Mary's labor lasted more than sixteen hours.
She began experiencing labor pains.

PropBank: labor.02
WordNet 3.0 Sense Numbers: 3

Sense Number 3: an organized political class of workers

Commentary: LABOR[+entity][+group][+people][+organized][+politically][+employee][-management]
NOTE: refers to non-management employees who are politically organized for their collective benefit.

Organized labor is not backing their party during this campaign.
That historian's specialty is European labor movements of the nineteenth century.
He is a well-know labor organizer.
The labor unions are planning a city-wide transportation strike.

PropBank: NM
WordNet 3.0 Sense Numbers: 1

Sense Number 4: people who are available as workers

Commentary: LABOR[+entity][+group][+people][+available][+for_work] [+relation][+role][+resource][+work]
NOTE: does not imply an organized political group, see Sense 3
NOTE: refers to the people doing the work, not the activity - see Sense 1

The size of the labor force is expected to shrink in coming decades.
They have outsourced the manufacturing to cheaper labor overseas.
These mothers are getting back into the labor pool when their children reach a certain age.

PropBank: NM
WordNet 0.0 Sense Numbers: 4b2