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

Class I. Words Expressing Abstract Relations
Section VIII. Causation
3. Power in Operation

170. Agency.

   NOUN:AGENCY, operation, force, working, strain, function, office, maintenance, exercise, work, swing, play; interworking, interaction; procuration, procurement.
  CAUSATION [See Cause]; mediation, intermediation, instrumentality [See Instrumentality]; conation, influence [See Influence]; action (voluntary) [See Action]; modus operandi [L.] [See Method].
  quickening -, maintaining -, sustaining- power; home stroke.
   VERB:BE IN ACTION &c. adj.; operate, work; act, act upon; perform, play, support, sustain, strain, maintain, take effect, quicken, strike.
  come -, bring- into -operation, – play; have play, have free play; bring to bear upon.
   ADJECTIVE:OPERATIVE, operant [rare], efficient, efficacious, practical, exertive, conative, effectual.
  at work, on foot; acting (doing) [See Action]; in operation, in force, in action, in play, in exercise; acted upon, wrought upon.
   ADVERB:BY THE AGENCY OF &c. n.; through (instrumentality) [See Instrumentality]; by means of [See Means].
  1. I myself must mix with action lest I wither by despair.—Tennyson
  2. The day is always his who works in it with serenity and great aims.—Emerson