subassembly
noun
sub·as·sem·bly ˌsəb-ə-ˈsem-blē 
: an assembled unit designed to be incorporated with other units in a finished product
Example Sentences
Recent Examples on the Web Using a 4-foot level, plumb each post and fasten the braces to the stakes to hold the subassembly in place. 
Joseph Truini, Popular Mechanics, 2 May 2020 Clamp this three-piece subassembly between the four-piece assembly on one side and the rest of the loose benchtop pieces on the other side. Richard Romanski, Popular Mechanics, 18 Jan. 2020
Joseph Truini, Popular Mechanics, 2 May 2020 Clamp this three-piece subassembly between the four-piece assembly on one side and the rest of the loose benchtop pieces on the other side. Richard Romanski, Popular Mechanics, 18 Jan. 2020 Word History
First Known Use
1908, in the meaning defined above