Definition
“A simple sentence contains a subject and a verb, and it may also have an object and modifiers. However, it contains only one independent clause.”
"Simple Sentences." Walden University, academicguides.waldenu.edu/writingcenter/grammar/sentencestructure#:~:text=A%20simple%20sentence%20contains%20a,contains%20only%20one%20independent%20clause. Accessed 29 Aug. 2022.
Informal Definition
A simple sentence is a basic sentence without multiple ideas/purposes and nothing beyond the singular use of a subject, verb, object, and additional simplistic grammatical forms.
Ex. I am tired.
Etymology
From the Latin sem (one) + plo (fold). We first see these two words in combination c.1200 in Latin as simplus, wretched, miserable and in the Old French as simple meaning plain, friendly, or simple-minded.
"simple (adj.)." Online Etymology Dictionary, 4 Oct. 2018, www.etymonline.com/word/simple. Accessed 29 Aug. 2022.