early 14c., toilen, "pull at, tug," from Anglo-French toiller, Old French toellier "pull or drag about" (see toil (n.1)). Intransitive meaning "struggle, work hard, labor for considerable time" is from late 14c., perhaps by influence of till (v.). Related: Toiled; toiling.
word-forming element used in making adjectives from nouns or adjectives (and sometimes verbs) and meaning "tending to; causing; to a considerable degree," from Old English -sum, identical with some, from PIE root *sem- (1) "one; as one, together with." Cognate with Old Frisian -sum, German -sam, Old Norse -samr; also related to same. "It usually indicates the possession of a considerable degree of the quality named: as mettlesome, full of mettle or spirit; gladsome, very glad or joyous" [Century Dictionary]. For the -some used with numbers (twosome, foursome, etc.), see -some (2).
<a href="https://www.etymonline.com/word/toilsome">Etymology of toilsome by etymonline</a>
Harper, D. (n.d.). Etymology of toilsome. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/toilsome