Mawson, C.O.S., ed. (1870–1938). Roget’s International Thesaurus. 1922.

Class I. Words Expressing Abstract Relations
Section VI. Time
2. Relative Time
1. Time with reference to Succession

120. Synchronism.

   NOUN:SYNCHRONISM; coexistence, coincidence; simultaneousness &c. adj.; concurrence, concomitance, unity of time, interim.
  [HAVING EQUAL TIMES] isochronism.
  CONTEMPORARY, coeval, coetanian [obs.].
   VERB:COEXIST, concur, accompany, go hand in hand, keep pace with; synchronize, isochronize.
   ADJECTIVE:SYNCHRONOUS, synchronal, synchronic or synchronical, synchronistic or synchronistical, simultaneous, coexisting, coincident, concomitant, concurrent; coeval, coevous [obs.]; contemporary, contemporaneous; coetaneous [rare], coinstantaneous, coterminous, collateral, coeternal; isochronous.
   ADVERB:AT THE SAME TIME; simultaneously &c. adj.; together, in concert, during the same time; in the same breath; pari passu [L.]; in the interim.
  at the very moment [See Instantaneity]; just as, as soon as; meanwhile (while) [See Time].