extension vs hold

extension and hold both are nouns.

Word	Noun	Adjective	Verb	Adverb
extension	Yes	No	No	No
hold	Yes	No	Yes	No

As nouns, hold is a hypernym of extension; that is, hold is a word with a broader meaning than extension:

extension: a mutually agreed delay in the date set for the completion of a job or payment of a debt
hold: time during which some action is awaited

Other hypernyms of extension include delay, postponement, time lag, wait.

extension (noun)	hold (noun)
an educational opportunity provided by colleges and universities to people who are not enrolled as regular students	the act of grasping
act of stretching or straightening out a flexed limb	the appendage to an object that is designed to be held in order to use or move it
act of expanding in scope; making more widely available	a cell in a jail or prison
an addition that extends a main building	the space in a ship or aircraft for storing cargo
an addition to the length of something	a stronghold
an additional telephone set that is connected to the same telephone line	power by which something or someone is affected or dominated
amount or degree or range to which something extends	understanding of the nature or meaning or quality or magnitude of something
the ability to raise the working leg high in the air	a state of being confined (usually for a short time)
the most direct or specific meaning of a word or expression; the class of objects that an expression refers to	time during which some action is awaited
a string of characters beginning with a period and followed by one or more letters; the optional second part of a PC computer filename
the spreading of something (a belief or practice) into new regions
a mutually agreed delay in the date set for the completion of a job or payment of a debt

extension (verb)	hold (verb)
	keep from exhaling or expelling
	keep in mind or convey as a conviction or view
	hold the attention of
	assert or affirm
	remain committed to
	declare to be
	bind by an obligation; cause to be indebted
	be in accord; be in agreement
	aim, point, or direct
	protect against a challenge or attack
	drink alcohol without showing ill effects
	have or hold in one's hands or grip
	be the physical support of; carry the weight of
	support or hold in a certain manner
	to close within bounds, or otherwise limit or deprive of free movement
	cover as for protection against noise or smell
	organize or be responsible for
	maintain (a theory, thoughts, or feelings)
	cause to come to an abrupt stop
	have or possess, either in a concrete or an abstract sense
	secure and keep for possible future use or application
	have rightfully; of rights, titles, and offices
	arrange for and reserve (something for someone else) in advance
	keep from departing
	take and maintain control over, often by violent means
	lessen the intensity of; temper; hold in restraint; hold or keep within limits
	cause to continue in a certain state, position, or activity
	remain in a certain state, position, or condition
	be valid, applicable, or true
	be pertinent or relevant or applicable
	have room for; hold without crowding
	have as a major characteristic
	resist or confront with resistance
	stop dealing with
	contain or hold; have within
	be capable of holding or containing