Definitions of a word can vary from one category of use or application area to another. For instance if we take the noun "root":
- In mathematics - A root of a particular number is another number that, when multiplied by itself one or more times, reaches that number and also A solution of some equations
- In gardening (biology) - The part of a plant that grows down into the earth to get water and food and holds the plant firm in the ground
- In anatomy - The part of a hair, tooth, or nail that is under the skin
- In linguistics - The root of a word is its most basic form, to which other parts, such as affixes, can be added
- In biblical use - A scion; a descendant
- In music - The fundamental note of a chord
- In computing - A user account with full and unrestricted access to a system
- Other - The cause or origin of something; The part of a thing attaching it to a greater or more fundamental whole; the end or base; An act of rooting (search unsystematically through an untidy mass or area; rummage)
As you can see the word "root" as a noun has very many definitions but some of them are general while others are specialized and that's why dictionaries try to categories these definitions.
Looking into Merriam-Webster's Dictionary (Root) we can see that:
For English Language Learners, Students and Kids the general definitions are:
- the part of a plant that grows underground, gets water from the ground, and holds the plant in place
- the part of a tooth, hair, fingernail, etc., that is attached to the body
- the cause or source of something
I perfectly agree with them since these are the common usages of this word in everyday life. What concerns understanding a definition of a word, here it much depends on the context, area of use and the audience. You would agree that in a dental office if somebody spoke the word "root" they would most probably be referring to "the part of a tooth" rather than anything different, wouldn't you? While in a mathematics class I doubt that somebody would mention something other than "A root of a particular number is another number that, when multiplied by itself one or more times, reaches that number" or "A solution of some equations"
These's also a difference in how they explain definitions to kids, students, language learners or others. For kids the definitions are usually brief, foolproof and written in the most simplest words. For language learners the definitions are usually very teachable and lucid. For students the definitions may be brief and plain, or expanded.
As for the word "less" for language learners, students and kids the common definitions are:
- comparative form of little (Adjective and Adverb)
- a smaller number or amount (Pronoun)