Noun

(en noun)

One who initiates

(chemistry) A substance that initiates a chain reaction or polymerization

(computing) A task (in a mainframe computer) that initiates multiple jobs

(medicine) A material whose presence in the body eventually leads to cancer

Noun

(en noun)

One who goes before, as into the wilderness, preparing the way for others to follow.

A person or other entity who is first or among the earliest in any field of inquiry, enterprise, or progress.

* {{quote-magazine, date=2013-05-10

, author=Audrey Garric , title=Urban canopies let nature bloom , volume=188, issue=22, page=30 , magazine=(The Guardian Weekly) citation , passage=As towns continue to grow, replanting vegetation has become a form of urban utopia and green roofs are spreading fast. Last year 1m square metres of plant-covered roofing was built in France, as much as in the US, and 10 times more than in Germany, the pioneer in this field.}}

Some people will consider their national heroes to be pioneers of civilization.

Certain politicians can be considered as pioneers of reform.

(obsolete, military)   A soldier detailed or employed to form roads, dig trenches, and make bridges, as an army advances; a sapper.

A member of any of several European organizations advocating abstinence from alcohol.

(Communism)   A child of 10–16 years in the former Soviet Union, in the second of the three stages in becoming a member of the Communist Party.