Today's Quintilian: 8.6.21-22

XXI. Quod genus non orationis modo ornatus sed etiam cotidiani sermonis usus recipit. Quidam synecdochen vocant et cum id in contextu sermonis quod tacetur accipimus: verbum enim ex verbis intellegi, quod inter vitia ellipsis vocatur: "Arcades ad portas ruere". Mihi hanc figuram esse magis placet, illic ergo reddetur. XXII. Aliud etiam intellegitur ex alio: "aspice, aratra iugo referunt suspensa iuvenci", unde apparet noctem adpropinquare. Id nescio an oratori conveniat nisi in argumentando, cum rei signum est: sed hoc ab elocutionis ratione distat.

21. This mode of expression not only adorns oratorical speeches, but finds its place even in common conservation [this must be a typo for 'conversation']. Some say that synecdoche is also used when we understand something that is not actually expressed in the words employed, as one word is then discovered from another. But this is sometimes numbered among defects in style under the name of ellipsis, as,

Arcades ad portas ruere;

The Arcadians to the gates began to rush;
22. I consider it rather a figure, and among figures it shall be noticed. But from a thing actually expressed another may be understood, as,

Aspice aratra jugo referunt suspensa juvenci,

Behold the oxen homeward, bring their ploughs
Suspended from the yoke,
whence it appears that night is approaching. I do not know whether this mode of expression is allowable to an orator, unless in argumentation, when one thing is shown to indicate another. But this has nothing to do with elocution.