subplot

From sub- +‎ plot.

English Wikipedia has an article on:

subplot

Wikipedia

subplot (plural subplots)

1. A plot within a story, subsidiary to the main plot.
   • 1978, R.B. Lee & R. Misiorowski, Script Models: A Handbook for the Media Writer,

     Subplot, a story line enclosed within the principal story to provide relief from the main plot's tension, add character dimension, etc.

   • 1998, Stephen Roy Miller, The Taming of a Shrew: the 1594 quarto:

     Structurally, the two most variant scenes (outside of Scene ii) are Scenes 3 and 4 in which the compiler works out the variant subplot.

   • 2001, Dennis O'Neil, The DC Comics Guide to Writing Comics:

     In a sense, Superman's romance with Lois Lane was a subplot and [...]

   • 2001, Nancy Arbuthnot Johnson, Vic Neufield, Forging Links for Health Research,

     But this story has a subplot — a subplot about fairness and how people have divergent levels of access to knowledge and resources.

2. A subdivision of a plot of land, especially one used for an agricultural experiment.
   • 1996, The American Midland Naturalist, the University of Notre Dame:

     [...] on sixteen 8/10-acre plots (12.8 acres) well distributed over the area. [...] A 1/160-acre subplot was established in a randomly chosen corner of each [...]

   • 1999, E. K. Sadanandan Nambiar, Christian Cossalter, Site Management and Productivity in Tropical Plantation Forest,

     There are 72 trees in each plot (6x12) and 36 trees in each subplot.

   • 2002, M. Boya Edwards, Proceedings for the Eight Biennial Southern Silvicultural Research Conference,

     Hardwood and shrub stems (besides gallberry) were counted by species and measured for total height (if greater than 2 ft) on 3 strip plots per subplot that were 0.01 acre […]

• underplot

subplot (third-person singular simple present subplots, present participle subplotting, simple past and past participle subplotted)

1. (transitive) To provide (a story) with a subplot.
   • 1965, Percival Hunt, The Gift of the Unicorn: Essays on Writing, page 70:

     In the pictures of places, too, an author uses economy; and for his plot, complicated and subplotted as it may seem, he cannot count on having vast stretches of eternity in which to elaborate forever.