strum on (something)
1. To play a stringed instrument by brushing or stroking the strings. A few of us were strumming on our guitars as we sat around the camp fire. It was such a classy wedding. They even hired someone to strum on a harp while the guests were being seated.
2. To play something, such as a chord or song, on a stringed instrument by brushing or stroking the strings. I never got past strumming a couple basic chords on the guitar. Anything more advanced than that was just too difficult for me. He loves strumming lighthearted melodies on his banjo.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
strum something on something
to brush or play with the fingers some stringed instrument, such as a guitar. She strummed a nice little melody on her guitar. He strummed the accompaniment on the guitar.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.