Definition of "entrain"

entrain¹

verb
third-person singular simple present entrains, present participle entraining, simple past and past participle entrained
1. To draw along as a current does.
2. (chemistry) To suspend small particles in the current of a fluid.
  Quotations
  In certain cases, it is possible to entrain enough of the solids continually in the effluent gas stream and then to disentrain them again away from the bed.
  1963, W. D. Jamrack, Rare metal extraction by chemical engineering techniques
3. (mathematics) To set up or propagate a signal, such as an oscillation.
4. (figuratively) To encarriage, to conjoin, to link; as in a series of entities, elements, objects or processes.
5. (neurobiology) To become trained or conditioned in a pattern of brain behavior.
  Quotations
  There are several neurofeedback-related approaches that make use of auditory and/or visual stimulation (AVS) to entrain or disentrain brain electrical activity.
  2007, James R. Evans, Handbook of Neurofeedback: Dynamics and Clinical Applications
  Hence, interestingly, a speaker (VR) might disentrain in no-frequency but entrain in the frequency of a particular discourse function; we also have a speaker with the opposite pattern (DF).
  2013, Simone Bassis, Anna Esposito, Francesco Carlo Morabito, Recent Advances of Neural Network Models and Applications

entrain²

verb
third-person singular simple present entrains, present participle entraining, simple past and past participle entrained
1. (poetic, intransitive) To get into or board a railway train.
  Quotations
  There were two further unscheduled stops, one at a small station, Skalice, where a small party of tourists entrained, and at Břeclav, a junction and customs post on the Austrian frontier.
  1947 January and February, Gerald Druce (Jun.), “A Journey on the "Slovak Arrow"”, in Railway Magazine, page 17
  [...] and the Southern Region has recently given another lead by adopting an approach practised for some time by certain U.S. commuter railroads - the pamphlet or brochure left on every seat at a rush-hour before passengers entrain.
  1959 April, “Talking of Trains: The S.R. tells the public”, in Trains Illustrated, page 174
2. (transitive) To put aboard a railway train.
  Quotations
  The train of articulated L.N.E.R. stock, of the type used on the London suburban services, which you have seen travelling empty over the Cheshire Lines Committee's main line through Trafford Park about midday in a westerly direction, was probably being sent to entrain workers from Risley (between Glazebrook and Padgate) at the conclusion of the morning shift.
  1946 March and April, “The Why and The Wherefore: L.N.E.R. Suburban Trains on the Cheshire Lines”, in Railway Magazine, page 129