Lineamentum (linea) is seen from the following parallel examples to have the same meaning as its noun stem: in geometria lineamenta, formae, intervalla, magnitudines sunt, De Or. I, 187; ignis rectis lineis in caelestem locum subvolat, T. 1, 40; lineamentum esse longitudinem latitudine carentem, Ac. II, 116; eam M. Varro ita definit: linea est, inquit, longitudo quaedam sine latidudine et altitudine, Gell. 1, 20, 7.
This detailed view of the _-mentum_ words gives occasion for making the following comment: the tendency of these nouns is to mean the instrument of an action, often the result of an action, rarely action itself. The verb stems are such as require an instrument for their action or suggest its result. The instrument is sometimes literal, sometimes figurative, and whether it is the one or the other is determined by the context. Given a verb stem which both suggests the result of action and requires an instrument, it is difficult to explain why a _-mentum_ noun formed on it should mean only instrument, and not result of action, or vice versa.
The list of _-bulum_ words is small, and they are nearly all concrete. Only two are abstract. As these two denote only figurative instruments, the treatment here will take no account of the division into concrete and abstract. There are two noun stem words. Three distinct classes of these words may be made, when viewed in relation to their verb stems: (1) Those denoting instrument; (2) Those denoting place; (3) Those denoting person. The second meaning is quite as common as the first, the third very rare (found only in two nouns).
1. NOUNS DENOTING INSTRUMENT.--Infundibulum (infundo) is an instrument for pouring from one vessel to another, a funnel: illa quae reflexa et resupina, more infundibuli per medullam transmittit quidquid aquarum superfluit, Col. 3, 18; in qua machina impedens infundibulum subministrat molis frumentum, Vitr. 10, 10.
Patibulum (pateo) is plainly an instrument, but having the _shape_ expressed by the verb stem, a fork-shaped yoke: dispessis manibus patibulum quom habebis, M. G. 360; caedes, patibula, ignes, cruces festinabant, Tac. A. 14, 33.
Rutabulum (ruo) is an instrument for raking or stirring up: iubebis rutabulo ligneo agitari quod decoxeris, Col. 12, 20. It occurs twice in Cato, in a list of other tools for use around a fire-place.