With examples show how its challenging to define the concept of "word" ?

1. Compound words: Compound words are formed by combining two or more words to create a new word with a different meaning. For example, "butterfly" is made up of "butter" and "fly," but it is considered a single word. This can make it challenging to define where one word ends and another begins.

2. Hyphenated words: Some words are hyphenated, such as "mother-in-law" or "self-esteem." These words can be considered single words or multiple words depending on the context, making it difficult to define them as a single unit.

3. Contractions: Contractions are formed by combining two words and omitting letters or sounds, such as "can't" for "cannot" or "I'm" for "I am." These can be challenging to define as single words because they are formed by combining multiple words.

4. Loanwords: Loanwords are words borrowed from other languages, such as "sushi" from Japanese or "pizza" from Italian. These words may not have direct equivalents in the borrowing language, making it difficult to define them as single words.

5. Neologisms: Neologisms are newly coined words or phrases that may not yet be widely recognized or accepted. For example, "selfie" or "twerk" were not commonly used words until recently. Defining these words as single units can be challenging because they may not have a long history or established meaning.