sup·​pos·​i·​ti·​tious sə-ˌpä-zə-ˈti-shəs How to pronounce supposititious (audio)
: fraudulently substituted : spurious
b of a child
: falsely presented as a genuine heir
: not recognized as lawful offspring
specifically : born to parents not married to each other
[influenced in meaning by supposition]
: of the nature of or based on a supposition : hypothetical
supposititiously adverb

Did you know?

The Latin verb supponere, meaning "substitute," has several legitimate heirs in English, including supposititious (which dates from the early 17th century) and supposition (a 15th-century addition). The "fraudulent" and "illegitimate" meanings of supposititious trace back to supponere in a fairly direct route, whereas the "imaginary" and "hypothetical" meanings were influenced by the meanings of supposition. In legal contexts, supposititious is primarily used in its earlier senses, as in "a supposititious (fraudulent) will" or "the child was supposititious (illegitimate)." When something hypothetical is being considered, the synonymous adjective suppositious is often preferred over supposititious.

Examples of supposititious in a Sentence

entered the world as the supposititious son of a rich lord

Word History


Latin suppositicius, from suppositus, past participle of supponere to substitute

First Known Use

1600, in the meaning defined at sense 1a

Time Traveler
The first known use of supposititious was in 1600


Dictionary Entries Near supposititious

Cite this Entry

“Supposititious.” Dictionary, Merriam-Webster, Accessed 28 Sep. 2023.

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