tewk-eyo-
“to keep touching, testing”touch, taste, tax, attain
Iterative yielding Latin taxāre, English touch, taste (via Old French), tax, attain.
Discussion
The PIE form *tewk-eyo- (to keep touching, testing) is an iterative derivative of *tewk- (to touch, to test by touching), with the *-eyo- suffix marking repeated action. The meaning is "to be in the habit of touching/testing" — an image of hands on goods, fingers checking quality, the sensory evaluation that precedes transaction.
The root produced two seemingly unrelated English word families that are in fact siblings: the taste/touch family and the tax/attain family — both united by the concept of evaluative contact.
Latin taxāre (to handle, to assess, to appraise by touch — the intensified form of tangere, "to touch") gave English tax (an assessed charge, literally a "touching" of your goods by the assessor), taste (from OF taster, "to touch, to feel, to try" — tasting was testing by touch of the tongue), and the legal term attach (ad-taxāre, to touch/seize upon, to lay hold of legally). The tax collector's assessment and the food taster's evaluation are the same PIE gesture: touching to determine value.
The French derivatives expanded the family: attain (ad-tangere via French ataindre, to reach/touch), tact (the sense of touch, hence diplomatic sensitivity — knowing what to touch and what to leave alone), contact (con-tangere, touching together), tangible (capable of being touched), and tangent (the line that touches a curve at exactly one point — one of the most elegant geometric metaphors, built on a PIE root about fingers on surfaces).
English touch itself descends through Old French tochier from a Vulgar Latin *toccāre of uncertain origin — possibly onomatopoeic, possibly related to this root through a different path. The semantic overlap is clear even if the direct etymological connection is debated.
The Italian descendant toccata (a keyboard composition designed to display the player's touch) and the fencing term touché ("touched!" — acknowledging a hit) preserve the physical-contact sense in artistic and martial contexts.
The legal and fiscal legacy of this root is its most consequential: the entire concept of taxation rests on the metaphor of the assessor's hand touching your property to determine its value. The Latin root taxāre evolved from physical evaluation to monetary assessment to compulsory payment — the hand that tests becomes the hand that takes.