Select the most appropriate one-word substitution for the given group of words.

If a word is composed of the first letters of the words in a sentence then it is called as 

Acronym

The most appropriate one-word substitution for "a word is composed of the first letters of the words in a sentence" is acronym.

• Shortform is a shortened version of a word or phrase.
• Simile is a figure of speech that compares two things using the words "like" or "as."
• Acronym is a word formed from the initial letters of a phrase.
• Alliteration is the repetition of initial consonant sounds in a sequence of words.

The word acronym comes from the Greek words "akros," meaning "tip" or "end," and "onyma," meaning "name." Acronyms are often used in technical and scientific fields, and they can also be used in everyday language.

Some examples of acronyms include:

• RADAR (Radio Detection and Ranging)