The word 'wearisome' is a compound formed within English from its native Germanic elements. Its first element, 'weary', descends from the Old English wērig, meaning "tired," which is itself of Germanic origin, possibly related to the concept of being worn down. The second element is the productive suffix '-some', from Old English -sum, akin to the modern English word 'some', which denotes the possession of a specified quality. Thus, the literal construction "characterized by weariness" logically evolved into its modern abstract sense of "causing weariness or boredom," describing something that induces a state of fatigue or tedium in a person.

Structure: weary + some - weary (Old English wērig, meaning "tired, exhausted"): The core adjective conveying the state of fatigue. - some (Old English -sum, an adjective-forming suffix meaning "characterized by, tending to"): A suffix that attaches to nouns, adjectives, or verbs to create adjectives describing a quality or tendency.