accidentals - used to raise or lower a pitch by a half-step (semitone). There are three types encountered in plainsong: flats (the most common, usually associated with the pitches b and e), sharps (uncommon), and naturals (also uncommon).

alignment - the degree of slant between the separated parts of a neume or quadratic character such as the climacus or scandicus.

arm - the broad vertical or slanted stroke of a neume or quadratic character connecting the two pitches of a descending melodic interval before an ascending shaft or note head.

aspect - general appearance of a hand or script. This is closely associated with its basic shape.

basic shape - the shape or element that influences all other characters in a notational style. The basic shape of a quadratic notation, for example, is square or slightly oblong.

bridge - Found especially in Italian scripts. It is the thin, slanted shaft between the foot and the second element in a scandicus or between the broad, quadratic heads and/or feet in pre-quadratic and quadratic notations.

clef - a letter or stylized symbol indicating the letter name of a pitch that corresponds to a penned, dry-point, or imagined line of a staff. These are most often found at the left-hand edge of a staff or staff line.

curve - there are five basic types of curves used in neumes:

• c-curve - curve arching towards the left, as in the letter "c."

• b-curve - curve arching towards the right, as in the letter "b."

• convex curve - curve that arches towards the top margin of the page.

• concave curve - curve that arches towards the bottom margin of the page.

• s-curve - two open curves joined and aligned more or less vertically with bowls arching in opposite directions, as in the letter "s."

custos (direct) pl. custodes - the symbol, often but not always resembling a check-mark, found at the right-hand extremity of the staff, that indicates the first pitch in the following line of music. The function of a custos is similar to that of a text catchword.

diastematic - musical notation that shows, through the use of staves or careful vertical placement, the pitches of notes. Non-diastematic notation does not indicate pitch height. See entry below for "in campo aperto."

finial (serif) - a small, decorative (or incidental) stroke at the top or bottom of a stem or shaft. As notational scripts developed, the finials in neumatic notations often became more and more substantial, eventually becoming note heads in quadratic notational scripts. When a finial becomes visually pronounced and signifies the precise point of a pitch in a diastematic notation, it may be described as a head. See entry for head below.

flexus - portion of a neumatic clivis or torculus that is attached to the upper part of a shaft and indicates a descending melodic interval. This usually consists of a single stroke, but there are some scripts in which the flexus consists of two separate strokes. See also preflexus below.

foot - in a vertically-aligned character, either quadratic or neumatic, the lowest horizontal stroke attached to the stem or shaft representing a pitch to be sounded. This occurs primarily on the pes and torculus characters.

head - the broad part or parts of a quadratic character centred on a staff line or space (whether drawn or assumed) representing the pitch to be sounded.

hinge - the part or parts of a neume connecting a flexus, preflexus, foot, or arm to a shaft. There are three basic types of hinges: continuous, abrupt, and reflexive.

• continuous - a hinge that is smooth and rounded in such a way that it is impossible to distinguish its exact point of departure from the shaft.

• abrupt- a hinge that is clearly attached to the shaft at an interior angle of 45° or greater.

• reflexive - a hinge that is clearly attached to the shaft at an interior angle of less than 45°

in campo aperto - literally "in an open field." Refers to notation that is non-diastematic (i.e. does not indicate precise pitches of notes).

liquescents - special signs and altered forms of the simple neumes frequently (though not exclusively) found over textual dipthongs, liquid consonants that are followed by consonants, or the word "et." These vary greatly in appearance. See character charts for more examples.

plica - in quadratic notations, an expressive (liquescent) ascender or descender emanating from the side of the note head horizontally opposite the stem. This takes many different forms. See the character charts for more examples.

preflexus - in a flexus consisting of two separate strokes, the first or connecting stroke between the two hinges.

shading - used to describe pen strokes. There are four basic descriptions: broad, thin, hairline, and tapered. See entry for "strokes" below.

shaft - in neumatic notations a single vertical stroke connecting or indicating pitches in an ascending pattern.

spica ("spike") - portion of a quadratic character's stem that ascends or descends beyond the note- head on the opposite side of its main ascending or descending section. A script that is characterized by many characters with spicae, such as is found in the "Fleury playbook," is "spicated."

staff (plstaves) - system of stacked, horizontal lines (which may or may not be entirely etched or penned) on which neumes or notes are written, and which indicate the pitches of notes.

stem - the primary thin, often hairline ascender or descender of a quadratic character.

stroke - strokes used to describe neumes are classified as broad, thin, hairline, or tapered.