Part of Speech: Verb, transitive
Meaning: 1. To insert new matter between parts of something else. 2. To adulterate or corrupt by adding new, irrelevant matter. 3. (Mathematics) To estimate a value that lies between two other values.
Notes: Interpolate has thrived since English borrowed it from Latin (See History). The action noun is interpolation and the agent noun, interpolator (watch the O in -or). You have your choice of adjectives: interpolative or interpolatory. Even though Interpol does interpolate wrong-doers in prison, the name of this well-known international police organization is unrelated.
In Play: Today's Good Word is a verb of insertion: "Now that her novel is a hit, Rhoda Book is happy that her editors interpolated it with so many of their own ideas." But as the second definition suggests, this verb often bears the pejorative connotation of irrelevance: "Every time Rhoda interpolates her opinion into a literary discussion, the discussion tends to skitter off course."
Word History: Today's word was all but traced from interpolatus, the past participle of Latin interpolare "to touch up, refurbish". It is related, of course, to extrapolate "to draw new information out of what is known". The original root of both words, believe it or not, is the same as that underlying yesterday's Good word, politesse! The PIE root was *pol-/pel- "hit, push", which also went into polish and polite. Interpolating and extrapolating are, of course, matters of pushing things into and out of others. (We hope that you can extrapolate from all this our gratitude to Susan Buce for interpolating today's word into our series.)
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