Inconstancy is a related term of swiftness.
As nouns the difference between inconstancy and swiftness
is that inconstancy is lack of constancy; lack of consistency in thought, emotion or action while swiftness is the state of being swift.
inconstancy
English
Noun
(
inconstancies)
Lack of constancy; lack of consistency in thought, emotion or action.
-
swiftness
English
Noun
(-)
the state of being swift
Synonyms
* celerity
* haste
* rapidity