rhythm phoneticPhoneticPhoneticPhoneticPhoneticPhoneticPhoneticPhoneticphonetic noun 
a strong pattern of sounds, words or musical notes which is used in music, poetry and dancing 
He beat out a jazz rhythm on the drums. [C]
She captures the rhythm of the poem exactly. [C]
I've got no sense of rhythm, so I'm a terrible dancer. [U]

Rhythm is also a regular movement. 
She was lulled to sleep by the gentle rhythm of the boat in the water.
The rhythm of the boat's motor became faster as it left the harbour.
By the second game, she was hitting the ball so hard that she didn't give the German player the opportunity to establish any rhythm.

Rhythm is also a regular pattern of change, esp. one which happens in nature. 
the rhythm of the seasons
Breathing and sleeping are examples of biological rhythms in human beings.

Rhythm and blues (also R & B) is a type of popular music of the 1940s and 1950s which has a strong beat. 
Rhythm and blues grew out of blues music and developed into rock and roll.

The rhythm method is a way of preventing pregnancy in which partners have sex on those days when the woman is unlikely to become pregnant. 
The rhythm method is one of the least successful methods of birth control.

The rhythm section of a dance or jazz group is the instruments that give a strong beat to the music. 
The drums and double bass usually form the rhythm section of a jazz group.

rhythmic, rhythmical phoneticPhoneticPhoneticPhoneticPhoneticPhoneticPhoneticPhoneticPhoneticphonetic adjective 
A sound which is rhythmic has a regular movement or beat which is repeated. 
The rhythmic sound of the train sent him to sleep.

rhythmically phoneticPhoneticPhoneticPhoneticPhoneticPhoneticPhoneticPhoneticPhoneticPhoneticPhoneticPhoneticphonetic adverb 
She tried to breathe deeply and rhythmically.
( Cambridge International Dictionary of English )