As a verb retain

is to keep in possession or use.

As a noun retentivity is

the ability to retain, potential for retention.

As nouns the difference between potential and retentivity

is that potential is while retentivity is the ability to retain, potential for retention.

As nouns the difference between capacity and retentivity

is that capacity is the ability to hold, receive or absorb while retentivity is the ability to retain, potential for retention.

As an adjective capacity

is filling the allotted space.

As nouns the difference between magnetism and retentivity

is that magnetism is the property of being magnetic while retentivity is the ability to retain, potential for retention.

Retentivity is a synonym of retentiveness.

As nouns the difference between retentiveness and retentivity

is that retentiveness is the state of being retentive while retentivity is the ability to retain, potential for retention.

Retentor is a related term of retentivity.

As nouns the difference between retentor and retentivity

is that retentor is a muscle which holds a body part in place, notably in extended or retracted position while retentivity is the ability to retain, potential for retention.

As an adjective muscle

is muscled, muscly, muscular.

As a verb muscle

is .

As a noun retentor is

a muscle which holds a body part in place, notably in extended or retracted position.

As a proper noun hold

is moon.

As a noun retentor is

a muscle which holds a body part in place, notably in extended or retracted position.

As a proper noun head

is , from residence near a hilltop or the head of a river, or a byname for someone with an odd-looking head.

As a noun wase is

(uk|dialect) a bundle of straw, or other material, to relieve the pressure of burdens carried upon the head.

In pathology|lang=en terms the difference between tubercle and apophysitis

is that tubercle is (pathology) a small rounded nodule forming the characteristic lesion of tuberculosis while apophysitis is (pathology) inflammation of an apophysis, a bony tubercle.

As nouns the difference between tubercle and apophysitis

is that tubercle is (anatomy) a round nodule, small eminence, or warty outgrowth, especially those found on bones for the attachment of a muscle or ligament or small elevations on the surface of a tooth while apophysitis is (pathology) inflammation of an apophysis, a bony tubercle.