plumb
Meaning
To measure the depth of something, especially water.
To test or examine something thoroughly to understand it.
To install and connect plumbing.
Exactly vertical.
Exactly, directly, or completely.
Usage
The sailor used a weighted line to plumb the depth of the harbor.
The book attempts to plumb the complexities of the human psyche.
She hung the picture perfectly plumb.
Etymology
The word 'plumb' descends directly from the Latin 'plumbum', the term for the dense, malleable metal lead. This etymological journey is a story of metonymy, where the material gave its name to the tool made from it: the 'plumbum' or lead weight. This weight, attached to a line, was used by builders and surveyors to determine a true vertical line or to measure depth, leading to the verb 'to plumb' and the adjective meaning 'perfectly vertical'. The modern abstract meanings of examining something thoroughly ('plumb the depths') or doing something exactly ('plumb in the middle') are logical extensions of this precise, probing, and direct physical action.
Analysis
The entire word 'plumb' is a simplex morpheme. It originates from the Latin 'plumbum', meaning 'lead' (the metal). In English, it functions as a noun, verb, adjective, and adverb, with its core semantic field relating to the use of a lead weight.