recruitment

The word was built in English from recruit plus the noun-forming -ment, with French recrutement as its counterpart, and every later sense keeps this core idea of bringing in new members. It names both the ongoing activity and a single round of hiring. In Rhodri Clark's 2019 railway report a spokesman speaks of "the recruitment of 72 new drivers": the of-phrase names the people brought in, not the organization doing the hiring.

Here the word turns countable and personal: each recruit has a recruitment, the particular way they were sought out. Pete Thamel, writing in 2009 about Tebow and Bradford, contrasts "their recruitments, offenses and personalities", and the plural marks separate stories rather than one shared activity. Describing words such as aggressive or gentle usually point to this sense rather than the general hiring process.

Population ecologists treat it as a tally of the young that survive to join the adult or breeding stock. They count it separately from gains through immigration, so it measures whether a population is replacing itself. The new individuals are themselves called recruits, which carries the military image into biology. It is typically measured in a particular stock or species over time, as in recruitment in a cod stock.

A respiratory physiologist's word for a lung opening all the way: regions that were airless or barely ventilated fill with air and begin to take part in gas exchange. It is usually spoken of as something to promote or achieve, as with deep breathing after surgery. The opposite state is collapse, which the ventilator technique is designed to reverse.

Where full aeration is a state the lung reaches, this is something done to it. In critical care the ventilator raises transpulmonary pressure briefly and under control, forcing collapsed alveoli back open in acute respiratory distress syndrome (ARDS). Clinicians speak of performing recruitment, and the skill lies in reopening the collapsed alveoli without overstretching healthy tissue.

Audiologists use the word for loudness that climbs too steeply. A sound just above the threshold of hearing may seem faint, yet a little more volume makes it overwhelming. The comfortable range shrinks from both ends, which is why the condition so often accompanies sensorineural hearing loss from cochlear damage. Despite sharing the word, it has nothing to do with the lung senses: nothing here is filled or reopened.