-able Also -ible and -uble; -ability, -ibility, and -ubility.
Able to be.
[Originally from the Latin adjectival suffix -bilis.]
The adjectival suffixes -able, -ible, and -uble have several meanings; the main one, and the usual one in new forms today, indicates an ability to do something (calculable, defensible, voluble), but other senses also exist: suitable for some purpose (reversible, edible); due to be (payable); having a quality expressed by the word stem (comfortable, passable, suitable); subject to (taxable); or causing some effect (terrible, horrible). Several hundred words contain these suffixes, of which a very few other examples are allowable, combustible, conceivable, enjoyable, gullible, legible, practicable, seasonable, soluble, visible, and washable.
The -ible and -uble endings are not currently active (and -uble is much less common than the others, with only soluble and voluble being at all common), but -able is frequently used to form new words, such as gluggable, of a wine that is good to drink; kebabable, a meat capable of being kebabed; or in Britain ISAble, of an investment that can be made into an ISA, an individual savings account. Part of the popularity of -able comes from its similarity to the English word able, though the two are not related.
The related suffixes -ability, -ibility, and -ubility form abstract nouns that refer to a quality, such as capability, plausibility, solubility, suitability, and usability.
A few adjectives have different meanings in their -able and -ible forms: contractable means ‘liable to be contracted’, as of a habit or a disease, but contractible means ‘able to be reduced in length’; forceable refers to a thing that can be forced open, whereas forcible means something executed by means of force; infusable is said of something, such as a herb, that can be steeped in water, while infusible refers to a thing that cannot be melted or fused.
Some words appear to contain these endings through accidents of spelling: crucible, double, parable, syllable, vegetable.