• thigmotropism •
thig-mê-tro-piz-êm • Hear it!
Part of Speech: Noun, mass (no plural)
Meaning: The ability of a plant (or other organism) to move when touched.
Notes: This Good Word is unrelated to thingamabobism "the frequent inability to think of the names for things" (like the word thigmotropism). It is, however, related to phototropism "the ability to move in the direction of light", hydrotropism "root growth toward water". This Good Word is used too seldom and in too narrow a context to have developed many relatives. There is an adjective, thigmotropic, which means that some plants may move thigmotropically. Do remember that the vowel in the middle is O, not A.
In Play: Perhaps the best known plant exhibiting thigmotropism is the Venus flytrap, whose wing-like leaves close in on any insect that lights on them. Touching the leaf of a mimosa results in its curling up and if you touch the leaf of a prayer plant, it will fold together with its partner as hands are folded in prayer.
Word History: Today's word refers to a "touch-turn" plant, based on Greek thigma "touch, handle" (from thinganein "to touch") + trope "turning" + ism, a noun suffix. Thigma is akin to Latin fingere "to touch, handle", unrelated to English finger, which shares an origin with Greek pent- "five", as in pentagon. Fingere also meant "to form" and in this sense its noun, fictio, fictionis "formation", went on to become English fiction.