
1) Ad-lib 2) Riffian 
Found on 
https://www.crosswordclues.com/clue/riff

1) Argentine rock music group 2) Berber 3) Berber of Moroccan coast 4) Berber of Morocco 5) Berber of the Moroccan coast 6) Berber tribesman 7) Bit of flashy guitar work 8) Bit of guitar 9) Bit of jazz 10) Comedic spiel 11) Comic comment 12) Fictional scientist 13) Guitar Hero challenge 14) Guitar highlight 
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https://www.crosswordclues.com/clue/riff

- a Berber living in northern Morocco
 - a jazz ostinato; usually provides a background for a solo improvisation
 
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A short repeated melodic phrase or 'signature' that is constructed to attract attention. Most riffs last for two bars but can vary from one to four bars in length. A classic riff can be heard on the introduction to '(I can't get no) Satisfaction' by the Rolling Stones.
Found on 
http://www.bbc.co.uk/radio2/soldonsong/glossary/r.shtml

A short melody repeatedly played in a tune (sometimes with variation) often between vocal lines.
Found on 
http://www.encyclo.co.uk/local/20447

A 
Berber people of northern Morocco, who under 
Abd al-Karim long resisted the Spanish and French. ...
Found on 
http://www.encyclo.co.uk/local/20688

Resource Interchange File Format [Microsoft]
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http://www.encyclo.co.uk/visitor-contributions.php

Riff is slang for a short, repeated sequence of musical notes, usually played on a guitar.
Found on 
http://www.probertencyclopaedia.com/browse/ZR.HTM

A riff is a short, repeated melodic pattern, and is often used in jazz. 
Found on 
http://www.violinonline.com/glossary.htm

[
n] - a Berber living in northern Morocco 2. [n] - a jazz ostinato
Found on 
http://www.webdictionary.co.uk/definition.php?query=riff

(1) A relatively simple, catchy repeated phrase. May be played behind a soloist or as part of a head. Often in a bluesy style. Riff tunes are made up of riffs, characteristic of the black bands of the 30s. (2) A pre-packaged phrase used by an improviser when he can't think of anything else, especially one which is especially catchy.
Found on 
https://www.apassion4jazz.net/glossary5.html

slang for a short, repeated sequence of musical notes, usually played on a guitar.
Found on 
https://www.easypacelearning.com/english-books/slang-words-a-to-z/375-slang
 noun a jazz ostinato; usually provides a background for a solo improvisation
Found on 
https://www.encyclo.co.uk/local/20974

A Berber people of northern Morocco, who under Abd al-Karim long resisted the Spanish and French
Found on 
https://www.encyclo.co.uk/local/21221

a repeated series of chords or notes, esp. on electric guitar - Justin wants to learn some heavy metal riffs.
Found on 
https://www.englishclub.com/vocabulary/music-vocabulary.htm
(Raster Image File Format) A file format used to store grayscale images.
Found on 
https://www.xrite.com/learning/other-resources/glossary
  No exact match found.