a large sandwich made of a long crusty roll split lengthwise and filled with meats and cheese (and tomato and onion and lettuce and condiments); different names are used in different sections of the United States
"After waiting an hour for my order, I finally took a big bite out of the sub and was ready to face the day."
A submarine.
"The captain ordered the sub to dive deep before making contact with enemy ships."
In plain English: A sub is a sandwich served on a long roll with ingredients like cold cuts, cheese, and vegetables.
"I ate a ham sub for lunch today."
be a substitute
"The young teacher had to substitute for the sick colleague"
"The skim milk substitutes for cream--we are on a strict diet"
To substitute for.
"The technician carefully subbed the glass slides with a thin layer of adhesive before applying the delicate circuitry."
To coat with a layer of adhering material; to planarize by means of such a coating.
In plain English: To sub means to take someone else's place temporarily, like covering for a friend when they can't make it.
"I will sub for my friend at work today because he is sick."
Usage: Use this verb when describing the process of applying a thin, adhering layer to smooth out surface irregularities on materials like silicon wafers or glass. It is specific to industrial manufacturing and should not be used for general meanings like shortening something or substituting an ingredient.
Under.
"The sub sandwich was slightly squashed under the weight of all the toppings."
The word sub is a shortened version of several different terms that originally began with the prefix sub- to indicate being under or below. It entered common usage as an informal abbreviation for these longer forms rather than evolving from a single original meaning.